The Greatest: Muhammad Ali through the years.

UNDATED: FORMER HEAVYWEIGHT CHAMPION MUHAMMAD ALI. Mandatory Credit: Gray Mortimore/ALLSPORT

The Greatest: Muhammad Ali through the years.

22 FEB 1992: MUHAMMAD ALI AT RINGSIDE DURING THE TERRY NORRIS VERSUS CARL DANIELS FIGHT IN SAN DIEGO, CALIFORNIA. Mandatory Credit: Holly Stein/ALLSPORT

The Greatest: Muhammad Ali through the years.

15 Sep 1978: Muhammad Ali wins his third World Heavyweight Title against Leon Spinks. Mandatory Credit: Allsport UK/Allsport

The Greatest: Muhammad Ali through the years.

UNDATED FILE PHOTO: Muhammad Ali and wife. (Photo by Diane Freed)

The Greatest: Muhammad Ali through the years.

1980: MUHAMMAD ALI GIVES A PRESS CONFERENCE BEFORE HIS FIGHT WITH LARRY HOLMES IN LAS VEGAS. Mandatory Credit: Steve Powell/ALLSPORT

The Greatest: Muhammad Ali through the years.

19 Apr 1991: MUHAMMAD ALI MAKES AN APPEARANCE AT THE BOUT BETWEEN EVANDER HOLYFIELD AND GEORGE FOREMAN IN ATLANTIC CITY, NEW JERSEY.

The Greatest: Muhammad Ali through the years.

UNDATED: MUHAMMAD ALI DURING A TRAINING SESSION. Mandatory Credit: Allsport UK/ALLSPORT

The Greatest: Muhammad Ali through the years.

Mar 1972: Boxer Muhammad Ali stands outside his house with his three kids. Mandatory Credit: Allsport USA /Allsport

The Greatest: Muhammad Ali through the years.

Undated: Muhammad Ali of the USA relaxes at home in Deer Lake, Pennsylvania, USA. Mandatory Credit: Allsport UK /Allsport

The Greatest: Muhammad Ali through the years.

SEP 1980: MUHAMMAD ALI AT HOME. Mandatory Credit: Allsport UK/ALLSPORT

The Greatest: Muhammad Ali through the years.

Mar 1990: Former heavyweight champion Muhammad Ali looks on with May-May Ali. Mandatory Credit: Ken Levine /Allsport

The Greatest: Muhammad Ali through the years.

7 Aug 1996: The Greatest meets the Greatest: Former World heavyweight champion Muhammad Ali takes on golfing legend Jack Nicklaus at a press conference during the final practise round at the US PGA Championships at the Valhalla Golf Club, Louisville, Kentucky, USA. Mandatory Credit: David Cannon/ALLSPORT

The Greatest: Muhammad Ali through the years.

Photo by Getty Images

1972: Muhammad Ali during training for his fight with Al 'Blue' Lewis held in Dublin, Republic of Ireland in 1972. (Photo by Getty Images)

The Greatest: Muhammad Ali through the years.

10 Feb 2002 - PHILADELPHIA: Jaime Fox and Muhammad Ali during the 2002 NBA All Star Game at the First Union Center in Philadelphia, Pennsylvania. NOTE TO USER: User expressly acknowledges and agrees that, by downloading and/or using this Photograph, User is consenting to the terms and conditions of the Getty Images License Agreement. Mandatory copyright notice: Copyright 2002 NBAE Mandatory Credit: Andy Hayt/NBAE/Getty Images

The Greatest: Muhammad Ali through the years.

405681 01: Actor Michael J. Fox (R) and boxer Muhammad Ali pretend to spar before giving their testimony before the Senate Appropriations Subcommittee on Health and Human Services May 22, 2002 in Washington, DC. Fox and Ali both have Parkinson's disease and would like Congress to put more money into finding a cure for the disease. (Photo by Mark Wilson/Getty Images)

The Greatest: Muhammad Ali through the years.

19 Jul 1996: Muhammad Ali holds the torch before lighting the Olympic Flame during the Opening Ceremony of the 1996 Centennial Olympic Games in Atlanta, Georgia. Mandatory Credit: Michael Cooper /Allsport

The Greatest: Muhammad Ali through the years.

MIAMI - DECEMBER 6: Boxing legend Muhammad Ali (L) gestures behind the head of actor Will Smith at the Miami Art Basel Taschen book premiere of Ali's new book, "GOAT - Greatest Of All Time" at the Miami Convention Center December 6, 2003 in Miami, Florida. (Photo by Gregorio Binuya/Getty Images)

The Greatest: Muhammad Ali through the years.

NEW YORK - JUNE 9: Boxer Muhammad Ali (L) lands an uppercut on actor Denzel Washington as they attend the Boys & Girls Clubs of America President's Dinner honoring Denzel Washington at the Waldorf Astoria June 9, 2004 in New York City. (Photo by Paul Hawthorne/Getty Images)

The Greatest: Muhammad Ali through the years.

1974: MUHAMMAD ALI OUTPOINTS JOE FRAZIER IN NEW YORK. Mandatory Credit: Allsport UK/ALLSPORT

The Greatest: Muhammad Ali through the years.

NEW YORK - MAY 5: Former New York City Mayor Rudolph Giuliani and Boxing great Muhammad Ali trade some punches backstage during the MTV Networks UpFront at The Theater at Madison Square Garden May 5, 2004 in New York City. (Photo by Matthew Peyton/Getty Images)

The Greatest: Muhammad Ali through the years.

HOUSTON - JULY 13: Muhammad Ali walks on to the field before he and the children of the Boys and Girls club throw out the first pitch before the Major League Baseball 75th All-Star Game at Minute Maid Park on July 13, 2004 in Houston, Texas. (Photo by Brian Bahr/Getty Images)

The Greatest: Muhammad Ali through the years.

Muhammad Ali at 'ROAST THIS! An Evening with Muhammad Ali and Friends' at the Century Plaza Hotel in Los Angeles, Ca. 11/16/00. (Photo by Kevin Winter/ImageDirect)

The Greatest: Muhammad Ali through the years.

LOS ANGELES - DECEMBER 2: Former heavyweight boxing champion Muhammad Ali gets a "punch" on the nose by actress Garcelle Beauvais Nilon at the Time To Give Gala benefiting the Afghanistan World Foundation and honoring Muhammad Ali with the Freedom Award on December 2, 2003 in Los Angeles, California. (Photo by Vince Bucci/Getty Images)

The Greatest: Muhammad Ali through the years.

Boxer Laila Ali poses with her father, former heavyweight champion Muhammad Ali, after she defeated Suzy Taylor in two rounds at the Aladdin Casino in Las Vegas, Nevada, August 17, 2002 (Photo By Scott Halleran/Getty Images)

The Greatest: Muhammad Ali through the years.

LOS ANGELES - AUGUST 2: Boxer Muhammad Ali (L) jokes with actor Tom Cruise (R) as they arrive at the world premiere of "Collateral" at the Orpheum Theatre August 2, 2004 in Los Angeles, California. (Photo by Kevin Winter/Getty Images)

The Greatest: Muhammad Ali through the years.

LOS ANGELES - AUGUST 2: Former heavyweight boxing champion Muhammad Ali and singer Diana Ross arrive at the World Premiere of "Collateral" at the Orpheum Theatre on August 2, 2004 in Los Angeles, California. (Photo by Kevin Winter/Getty Images)

The Greatest: Muhammad Ali through the years.

ATLANTA, UNITED STATES: Former world heavyweight boxing champion and 1960 Olympic gold medalist Muhammad Ali (L) is congratulated by International Olympic Committee President Juan Antonio Samaranch after receiving a replacement gold medal for his 1960 win, at halftime of the gold medal basketball game between the US and Yugoslavia, 03 August. Ali had thrown the original medal into the Ohio River when he was criticized for not fighting in Vietnam. ELECTRONIC IMAGE (FOR EDITORIAL USE ONLY) AFP-IOPP/Tim CLARY (Photo credit should read TIM CLARY/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

ATLANTA, UNITED STATES: Former world heavy-weight champion Muhammad Ali acknowledges the applause of the public while attending the men's Olympic final at the Alexander Memorial Coliseum in Atlanta, Georgia, 04 Aug. (FOR EDITORIAL USE ONLY) (Photo credit should read OMAR TORRES/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

HANOI, VIET NAM: Former heavyweight boxing champion Mohammed Ali (L), meets with Vu Chi Cong, deputy head of the Foreign Ministry's American Department in Hanoi, Vietnam 11 May 1994. Ali, once convicted for refusing to serve in the US military during the Vietnam War, arrived 10 May for a five-day goodwill visit aimed at helping resolve the MIA issue. (Photo credit should read Hoang Dinh NAM/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

VERONA, : File photo dated 08 October 1999, shows boxing great Muhammad Ali at the ringside before the match of his daugher Laila Ali and April Fowler at the Turning Stone Casino Resort in Verona, New York. Ali said in an interview with Newsweek magazine that hit the newsstands 18 October 1999, that he planned to fight, a 15-round exhibition bout despite suffering from Parkinson's disease. AFP PHOTO/FILES/Stan HONDA (Photo credit should read STAN HONDA/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

NEW YORK, UNITED STATES: Muhammad Ali touches a younger version of himself which is on the special edition Muhammad Ali Wheaties' box that marks the cereal's 75th anniversary 04 February. Wheaties, "The Breakfast of Champions," is honoring the man widely accepted as one of the greatest athletes of all time. AFP PHOTOS/Henny Ray ABRAMS (Photo credit should read HENNY RAY ABRAMS/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

LAS VEGAS, : Former heavyweight boxing champion Mike Tyson (L) speaks with boxing legend Muhammad Ali, 22 February, at the University of Nevada, Las Vegas (UNLV) student union ballroom. During the evening's program, which kicked-off Black History Month, Ali was honored for the contributions he made to the African-American community. The appearance was arranged by Ali's daughter, Maryum Ali, who attends UNLV, and the Black Student Association at UNLV. AFP PHOTO John GURZINSKI (Photo credit should read JOHN GURZINSKI/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

LOS ANGELES, UNITED STATES: Boxing legend Muhammad Ali (L) poses with actor Dustin Hoffman as they arrive for "Roast This! An Evening with Muhammad Ali and Friends", a celebrity roast of Ali 16 November, 2000 in Los Angeles, Ca. The benefit event raised over three million USD for the Muhammad Ali Center in Louisville, Kentucy. AFP PHOTO/VINCE BUCCI (Photo credit should read Vince Bucci/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

NEW YORK, UNITED STATES: Former boxer Muhammad Ali (C) is joined by his wife Lonnie (R) and New York Mayor Rudy Giuliani (L) in Times Square 31 December 2000. Ali pressed the button to lower the ball marking the start of the new year. AFP PHOTO Doug KANTER (Photo credit should read DOUG KANTER/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

NEW YORK, UNITED STATES: Heavyweight boxing legend Muhammad Ali (L) and present heavyweight title-holder Evander Holyfield (R) talk at a reception before the Time Magazine 75th Anniversary celebration at Radio City Music Hall 03 March in New York. More than 90 Time cover subjects are attending the event along with a tribute by President Clinton. Time was first published in 1923. AFP PHOTO Timothy A. Clary (Photo credit should read TIMOTHY A. CLARY/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

LOS ANGELES, UNITED STATES: US former world heavyweight boxing champion Muhammad Ali (L) jokes with US actor Will Smith (R) who portrays him in new film "Ali," at the movie's premiere in Hollywood, CA, 12 December 2001. AFP PHOTO/Lucy NICHOLSON (Photo credit should read LUCY NICHOLSON/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

WASHINGTON, : Former heavyweight boxing champ Muhammad Ali throws a punch as he poses for photographers on his arrival at the Uptown Theatre in Washington, DC, with his wife, Lonnie, for the premiere of "Ali", the screen biography of his life, 17 December, 2001. Actor Will Smith portrays Ali as the controversial boxer, who started his career as Cassius Clay before converting to Islam and changing his name. AFP PHOTO/Mike THEILER (Photo credit should read MIKE THEILER/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

UNDATED: JOE FRAZIER, GEORGE FOREMAN AND MUHAMMAD ALI. Mandatory Credit: Gray Mortimore/ALLSPORT

The Greatest: Muhammad Ali through the years.

LOS ANGELES, UNITED STATES: US former world heavyweight boxing champion Muhammad Ali gives a humorous speech before a star is unveiled for him on the Hollywood Walk of Fame, in Los Angeles, CA, 11 January 2002. AFP PHOTO/LUCY NICHOLSON (Photo credit should read LUCY NICHOLSON/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

NEW YORK, NY - APRIL 1: Heavyweight champion Floyd Patterson (R) rubs heavyweight champion Muhammad Ali's shoulder as he says hello 01 April 1993 at a gathering of boxers for the World Boxing Council awards ceremony. (Photo credit should read MARIA BASTONE/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

PHOENIX - APRIL 2: Former heavyweight boxing champion Muhammad Ali strikes a pose as actor Chevy Chase watches upon arriving at Celebrity Fight Night XI April 2, 2005 at Arizona Biltmore Resort & Spa in Phoenix, Arizona. The charity event raises money to battle Parkinson's disease. (Photo by Jeff Topping/Getty Images)

The Greatest: Muhammad Ali through the years.

SINGAPORE - JULY 05: Mayor of New York Michael Bloomberg welcomes boxing legend Muhammad Ali during a NYC2012 press conference on July 5, 2005 in Singapore. The 117th International Olympic Committee session starts on July 6 with the announcement of the city which will host the 2012 Summer Games. The cities up for the bid are London, Madrid, Moscow, New York and Paris. (Photo by Andrew Wong/Getty Images)

The Greatest: Muhammad Ali through the years.

QUITO, ECUADOR - DECEMBER 17: Legendary US boxer Mohammed Ali (R) is kissed by a young Ecuadoran girl late, 17 December 1994, at the Quito's Ruminahui Coliseum, Ecuador. Ali was attending the World Boxing Association's super middleweight title fight between US boxers Frank Liles and Michael Nunn. (Photo credit should read FERNANDO ARAUJO/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

NEW YORK - DECEMBER 2: Former heavyweight champ Muhammad Ali (L) and actor Tony Danza make an appearance at Barnes and Noble to meet fans and to promote Muhammad's new book, "The Soul of a Butterfly" on December 2, 2004 in New York City. (Photo by Peter Kramer/Getty Images)

The Greatest: Muhammad Ali through the years.

LOUISVILLE, KY - SEPTEMBER 20: Former World Heavyweight Champion Muhammad Ali mock boxes with a young challenger during the Muhammad Ali Tribute charity event 20 September at Freedom Hall in Louisville, KY. Bidders could vie to go into the ring and "fight" with Ali or other fighters. (Photo credit should read JOHN RUTHROFF/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

LOS ANGELES - JULY 13: (L to R) Howard Bingham with founder and host Earvin "Magic" Johnson and boxer Muhammad Ali joke around on stage during the 20th Annual "Midsummer Night's Magic Awards Dinner" on July 13, 2005 at the Century Plaza Hotel in Los Angeles, California. (Photo by Amanda Edwards/Getty Images)

The Greatest: Muhammad Ali through the years.

PHOENIX, AZ - MARCH 18: Muhammad Ali puts "rabbit ears" up behind Jim Carrey's head as he presents Carrey with the Muhammad Ali Celebrity Entertainer award at Celebrity Fight Night XII March 18, 2006 at the JW Marriott Desert Ridge Resort & Spa in Phoenix, Arizona (Photo by Will Powers/Getty Images)

The Greatest: Muhammad Ali through the years.

ATLANTA, GA - DECEMBER 2: Former 1968 Olympic gold medalist Muhammad Ali lights the first torch to start the Olympic Torch Relay 04 December 2001, at Centennial Olympic Park in Atlanta, Georgia. (Photo credit should read CHRIS STANFORD/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

PARIS, FRANCE - 1978: American boxer Muhammad Ali (aka Cassius Clay) speaks during an interview for a French television program 1978 in Paris, France. (Photo by Patrick Riviere/Getty Images)

The Greatest: Muhammad Ali through the years.

NEW YORK - NOVEMBER 11: (L-R) Tracy Pollan, actor Michael J. Fox and Muhammad Ali pose at "A Funny Thing Happened On The Way To Cure Parkinson's" benefit gala at the Waldorf-Astoria on November 11, 2006 in New York City. (Photo by Evan Agostini/Getty Images)

The Greatest: Muhammad Ali through the years.

KINSHASA, CONGO - OCTOBER 30: A general view of "The Match of the Century " between the former world heavyweight boxing champion the American Muhammad Ali (R) and his compatriot and titleholder George Foreman (L). Ali won and got back his title October 30, 1974 in Kinshasa, Congo. (Photo by: AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

PHOENIX - MARCH 28: Muhammad Ali (L) and musician Jon Bon Jovi pose during Muhammad Ali's Celebrity Fight Night XV held at the JW Marriott Desert Ridge Resort & Spa on March 28, 2009 in Phoenix, Arizona. (Photo by Getty Images/Getty Images for Celebrity Fight Night)

The Greatest: Muhammad Ali through the years.

LOS ANGELES - JULY 13: Honoree and Rev. Jesse Jackson and honoree and boxer Muhammad Ali arrive at the 20th Annual "Midsummer Night's Magic Awards Dinner" on July 13, 2005 at the Century Plaza Hotel in Los Angeles, California. (Photo by Amanda Edwards/Getty Images)

The Greatest: Muhammad Ali through the years.

PARIS, FRANCE - 1978: American boxer Muhammad Ali (aka Cassius Clay) speaks during an interview for a French television program 1978 in Paris, France. (Photo by Patrick Riviere/Getty Images)

The Greatest: Muhammad Ali through the years.

JOHANNESBURG, SOUTH AFRICA - APRIL 10: Boxing legend Mohammed Ali (L) shakes hands 10 April 1993 with traditional dancers upon arrival in South Africa. Ali also met with the nation's black and Moslem leaders as South Africa was schocked by the assassination of the Communist Party leader Chris Hani. (Photo credit should read STR/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

BEVERLY HILLS, CA - DECEMBER 10: Retired boxer Muhammad Ali, actress Angelina Jolie, and actor Brad Pitt attend the UNICEF Ball honoring Jerry Weintraub held at the Beverly Wilshire Hotel on December 10, 2009 in Beverly Hills, California. (Photo by Kevin Winter/Getty Images for UNICEF)

The Greatest: Muhammad Ali through the years.

PHOENIX - MARCH 20: Muhammad Ali attends Celebrity Fight Night XVI on March 20, 2010 at the JW Marriott Desert Ridge in Phoenix, Arizona. (Photo by Michael Buckner/Getty Images for Celebrity Fight Night)

The Greatest: Muhammad Ali through the years.

CINCINNATI, OH - JUNE 20: Entertainer Bill Cosby (right) sits with former heavyweight boxing champion Muhammad Ali before both received Major League Baseball Beacon Awards prior to the Gillette Civil Right Game between the Cincinnati Reds and Chicago White Sox at Great American Ball Park on June 20, 2009 in Cincinnati, Ohio. (Photo by Joe Robbins/Getty Images)

The Greatest: Muhammad Ali through the years.

photo datée des années 60 de l'ancien champion du monde de boxe dans la catégorie des poids lourds, Mohammed Ali (Cassius Clay). Mohammed Ali devint champion olympique des poids mi-lourds en 1960 puis champion du monde poids lourds pour la première fois en février 1964 contre Sonny Liston. Picture dated from the 60's of the U.S. boxing champion Cassius Clay (Muhammad Ali), who got the Olympic middle heavyweight gold meadal in 1960 in Rome, aged 18, and got the professional world heavyweight title for the first time in February 1964 against Sonny Liston. (Photo credit should read -/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

PHOENIX - MARCH 20: Producer Randy Jackson (L) and Muhammad Ali attend Celebrity Fight Night XVI on March 20, 2010 at the JW Marriott Desert Ridge in Phoenix, Arizona. (Photo by Michael Buckner/Getty Images for Celebrity Fight Night)

The Greatest: Muhammad Ali through the years.

NEW YORK - NOVEMBER 13: (EXCLUSIVE ACCESS - PREMIUM RATES APPLY) Muhammad Ali onstage during the Michael J. Fox Foundation's 2010 Benefit "A Funny Thing Happened on the Way to Cure Parkinson's" at The Waldorf=Astoria on November 13, 2010 in New York City. (Photo by Andrew H. Walker/Getty Images for the Michael J. Fox Foundation for Parkinson's Research)

The Greatest: Muhammad Ali through the years.

PHOENIX, AZ - MARCH 19: Muhammad Ali and honoree Halle Berry attend Muhammad Ali's Celebrity Fight Night XVII at JW Marriot Desert Ridge Resort & Spa on March 19, 2011 in Phoenix, Arizona. (Photo by Michael Buckner/Getty Images for Celebrity Fight Night)

The Greatest: Muhammad Ali through the years.

UNITED STATES - NOVEMBER 09: Muhammad Ali and President George W. Bush at the Freedom Awards Ceremony at the White House in Washington D.C. on November 9, 2005. (Photo by Douglas A. Sonders/Getty Images)

The Greatest: Muhammad Ali through the years.

World Heavyweight Boxing Champion Muhammad Ali attends a news conference at the National Press Club on May 24, 2011 in Washington, DC. Ali and other prominent American Muslims and clergy appealed to Iran's Supreme Leader for the release Shane Bauer and Josh Fattal, the two U.S. hikers detained in Iran since July 31, 2009. AFP PHOTO/YURI GRIPAS (Photo credit should read YURI GRIPAS/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

Muhammad Ali and LeRoy Neiman during Muhammad Ali and LeRoy Neiman at Ballys Hotel Honoring Neimans paintings of Muhammed Ali at Ballys Hotel in Las Vegas, Nevada, United States. (Photo by Denise Truscello/WireImage)

The Greatest: Muhammad Ali through the years.

World heavyweight champion Muhammad Ali works out at the Fifth Street Gym, Miami Beach, Florida (Photo by A. Messerschmidt/Getty Images)

The Greatest: Muhammad Ali through the years.

Muhammad Ali during training on 10 July 1972 for his fight with Al 'Blue' Lewis held at Croke Park in Dublin, Republic of Ireland. (Photo by Don Morley/Getty Images)

The Greatest: Muhammad Ali through the years.

Muhammad Ali during training on 10 July 1972 for his fight with Al 'Blue' Lewis held at Croke Park in Dublin, Republic of Ireland. (Photo by Don Morley/Getty Images)

The Greatest: Muhammad Ali through the years.

WASHINGTON, DC - JANUARY 8: US President Bill Clinton presents boxing legend Muhammad Ali with the Presidential Citizens Medal during ceremonies 08 January 2001 at the White House in Washington, DC. Ali was one of 28 honorees recognized for remarkable service and accomplishments in a variety of fields. (Photo credit should read STEVE JAFFE/AFP/Getty Images)

The Greatest: Muhammad Ali through the years.

Moroccan King Hassan II (R) salutes former World Heavyweight Champion Mohamed Ali after decorating him in a ceremony in the Royal Palace in Rabat 15 January. The former Cassius Clay was visiting Morocco for four days at the king's invitation to participate in royal ceremonies for the holy fasting month of Ramadan. (Photo credit should read ABDELHAK SENNA/AFP/Getty Images)