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PHOENIX -- Boxing legend Muhammad Ali has passed away after being hospitalized with respiratory problems recently, according to multiple national media reports.
Ali, 74, was a three-time World Heavyweight Champion.
He became interested in boxing after reporting the theft of his bike to a policeman who gave boxing lessons at a local community center.
As an amateur boxer, Cassius Clay -- as he was known then -- won 100 of 108 fights, including six Kentucky Golden Gloves championships.
In February 1964, he defeated Sonny Liston for the title of World Heavyweight Champion.
In the “Rumble in the Jungle” in October 1974 in Kinshasa, Zaire, Ali defeated George Foreman to again become the World Heavyweight Champion.
Ali became the World Heavyweight Champion for the third time in September 1978 when he defeated Leon Spinks.
In 1979, Ali retired from professional boxing.
Ali revealed in 1984 that he had Parkinson’s disease.
Ali leaves behind his wife, Yolanda “Lonnie” Williams, and nine children.
The winners of the 1960 Olympic medals for light heavyweight boxing on the winners' podium at Rome: Cassius Clay (now Muhammad Ali) (C), gold; Zbigniew Pietrzykowski of Poland (R), silver; and Giulio Saraudi (Italy) and Anthony Madigan (Australia), joint bronze. (Photo by Central Press/Getty Images) 
1964: Heavyweight Boxing Champion of the World, Cassius Clay, who later changed his name to Muhammad Ali. (Photo by Harry Benson/Getty Images) 
7th August 1966: American boxer Muhammad Ali, formerly Cassius Clay, leaves the Cumberland Hotel for the USA after defeating Brian London. (Photo by Clive Limpkin/Express/Getty Images) 
29th November 1974: American boxer Muhammad Ali, formerly Cassius Clay, strikes an aggressive pose at a press conference. (Photo by Harry Dempster/Express/Getty Images) 
22nd February 1964: British pop group The Beatles, from left to right; Ringo Starr, John Lennon (1940 - 1980), George Harrison (1943 - 2001) and Paul McCartney; in the ring with champion American boxer Cassius Clay, whilst in Miami. (Photo by Keystone/Getty Images) 
25th February 1964: US boxers Cassius Clay (Muhammad Ali) and Sonny Liston (right) during their world heavyweight title fight at Miami Beach, Florida, which Ali went on to win. (Photo by Harry Benson/Express/Getty Images) 
25th February 1964: American boxer Cassius Clay (left), later Muhammad Ali, in action against Sonny Liston during their heavyweight title fight at Miami Beach, Florida. Clay won the contest, becoming world champion, when Liston failed to come out at the start of the seventh round. (Photo by Harry Benson/Express/Getty Images) 
25th February 1964: American boxer Cassius Clay, later Muhammad Ali, celebrates his win over Sonny Liston in their heavyweight title fight at Miami Beach, Florida. Clay won the contest, becoming world champion for the first time, when Liston failed to come out at the start of the seventh round. (Photo by Harry Benson/Express/Getty Images) 
WASHINGTON, : US President Bill Clinton leans on former world boxing heavyweight champion Muhammad Ali (R) at the National Italian American Foundation (NIAF) 25th Anniversary Awards Gala Dinner at a Washington DC hotel 28 October, 2000. Ali and his trainer Angelo Dundee were honored with the NIAF One America award at the gathering. Founded in 1975 as a non-profit, non-partisan foundation, the NIAF works to preserve and protect Italian American heritage and culture. AFP PHOTO/Manny CENETA (Photo credit should read MANNY CENETA/AFP/Getty Images) 
Heavyweight boxing champion Muhammad Ali looks at a book with his manager Angelo Dundee, 25th June 1975. (Photo by Evening Standard/Hulton Archive/Getty Images) 
WASHINGTON - NOVEMBER 09: U.S. President George W. Bush presents former heavy weight boxing champion Muhammad Ali (L) with the Medal of Freedom during a ceremony during a ceremony in the East Romm of the White House November 9, 2005 in Washington, DC. Bush presented 14 Medals of Freedom to recipients including retiring Federal Reserve Chairman Alan Greenspan and Aretha Franklin during the ceremony. (Photo by Mark Wilson/Getty Images) 
LAS VEGAS, NV - FEBRUARY 18: (EXCLUSIVE COVERAGE) Boxing legend Muhammad Ali (L) and wife Lonnie Ali appear onstage during the Keep Memory Alive foundation's "Power of Love Gala" celebrating Muhammad Ali's 70th birthday at the MGM Grand Garden Arena February 18, 2012 in Las Vegas, Nevada. The event benefits the Cleveland Clinic Lou Ruvo Center for Brain Health and the Muhammad Ali Center. (Photo by Ethan Miller/Getty Images for Keep Memory Alive) 
LONDON, ENGLAND - JULY 26: Former US Olympic boxer Muhammad Ali attends the U.S. Olympic Committee Benefit Gala at USA House at the Royal College of Art on July 26, 2012 in London, England. (Photo by Joe Scarnici/Joe Scarnici/Getty Images) 
Montage de deux photos du boxeur am?ricain Mohamed Ali (Cassius Clay) prises ? Kinshasa, le 27 octobre 1974, lors d'une s?ance d'entra?nement quelques jours avant le match ? l'issu duquel il regagnera son titre de champion du monde de boxe des poids lourds contre son compatriote George Foreman. Photo de gauche, sa m?re prend soin de Mohammed Ali. Photo de droite : Mohamed Ali r?pond aux journalistes. Combo of two pictures of former heavyweight boxing champion Muhammad Ali (Left picture) with his mother taking care of him during a training session and (right picture) and as he answers to journalists questions September 27 1974 in Kinshasa a few days before the fight he was to win against George Foreman. (Photo credit should read -/AFP/Getty Images) 
Le boxeur am?ricain Mohamed Ali (Cassius Clay) triomphe et devient champion du monde de boxe des poids lourds le 30 octobre 1974 ? Kinshasa ? l'issu du combat qui l'opposait au tenant du titre George Foreman. Muhammad Ali (Cassius Clay) (L) raises his arms as he just won the title of heavyweight boxing champion against his compatriot and titlehoder George Foreman (R) in Kinshasa October 30 1974. (Photo credit should read -/AFP/Getty Images) 
Le champion du monde de boxe des poids lourds am?ricain George Foreman (C) pousse son compatriote Mohamed Ali (Cassius Clay) (D) dans les cordes sous le regard de l'arbitre (G) ? Kinshasa le 30 octobre 1974 lors du combat ? l'issu duquel Mohamed Ali, reprenant l'offensive, lui ravira son titre. A picture taken September 30 1974 in Kinshasa of the fight opposing former world heavyweight boxing champion the American Muhammad Ali (R) and his compatriot and titleholder George Foreman (C). Ali won and got back his title. (Photo credit should read -/AFP/Getty Images) 
Combat ? l'issu duquel Mohamed Ali (Cassius Clay) (G) conservait son titre de champion du monde de boxe des poids lourds face ? son compatriote Ken Norton (D), le 28 septembre 1976, au Yankee Stadium de New York. Les juges le d?clar?rent vainqueur aux points apr?s le 15?me round. An action of the fight at the end of which he American Muhammad Ali (Cassius Clay) (L) kept his title of heavyweight boxing world champion against his compatriot Ken Norton at the Yankee Stadium of New York September 09 1976. (Photo credit should read -/AFP/Getty Images) 
A picture taken March 08 1971 in New York at the Madison Square Garden of the heavyweight boxing world championship fight between Muhammad Ali (Cassius Clay) (on the floor) and Joe Fazier at the end of which Frazier kept his title of heavyweight boxing world champion. (Photo credit should read -/AFP/Getty Images) 
NEW YORK, NY - OCTOBER 04: Former boxing champion Muhammad Ali attends the Norman Mailer Center 4th Annual Benefit Gala on October 4, 2012 in New York City. (Photo by Cindy Ord/Getty Images for Norman Mailer Center) 
Former world heavyweight champion Muhammad Ali (L) and titleholder US George Foreman (R) fight on October 30, 1974 in Kinshasa, Zaire during their world heavyweight championship match. Ali won by knocking out Foreman in the eighth round. (Photo credit should read -/AFP/Getty Images) 
US former heavyweight boxing champion Muhammad Ali gives a punch in front of photographers at hotel Belvedere in Davos 28 January 2006. AFP PHOTO ERIC FEFERBERG (Photo credit should read ERIC FEFERBERG/AFP/Getty Images) 
In this photo taken on October 27, 1974 US boxing heavyweight champion Muhammad Ali (born Cassius Clay) gestures during a press conference three days before the heavy weight world championship in Kinshasa. On October 30, 1974 Muhammad Ali knocked out George Foreman in a clash of titans known as the "Rumble in the Jungle", watched by 60 000 people in the stadium in Kinshasa and millions elsewhere. AFP PHOTO (Photo credit should read STR/AFP/Getty Images) 
TO GO WITH AFP STORIES In this photo taken on October 30, 1974 shows US boxing heavyweight champion Muhammad Ali (C) (born Cassius Clay) during a press conference after the heavyweight world championship in Kinshasa. On October 30, 1974 Muhammad Ali knocked out George Foreman in a clash of titans known as the "Rumble in the Jungle", watched by 60 000 people in the stadium in Kinshasa and millions elsewhere AFP PHOTO (Photo credit should read STR/AFP/Getty Images) 
27 Feb 1964: Cassius Clay (Muhammad Ali) flies around the ring after beating Sonny Liston in the seventh round of the World Heavyweight Title bout in Miami Beach, Florida, USA. It was during these scenes that Clay claimed, "I am the Greatest" and "I shook up the World". Mandatory Credit: Allsport Hulton/Archive 
American boxer Cassius Clay (now Muhammad Ali) trains for his World Heavyweight Boxing Championship fight against fellow American Sonny Liston at Miami Beach, Florida. Original Publication: People Disc - HW0519 (Photo by Harry Benson/Getty Images)
CNN contributed to this report.
