One of Muhammad Ali's world boxing championship belts sold at auction for $6.18 million to NFL team owner

• An NFL franchise owner bought one of Muhammad Ali's historic boxing belts at auction.
• The belt for sale was the championship Ali won when he beat George Foreman in 1975.

One of Muhammad Ali's old world boxing championship belts has been bought at auction for $6.18 million.

Ali died aged 74 in 2016 from septic shock and respiratory illness. He was known around the world for his Hall of Fame boxing career, larger-than-life celebrity, and political activism.

During his heyday in the 1960s and 1970s he fought a who's who of heavyweight greats, taking part in some of the most famous boxing events of all time.

He beat Sonny Liston, Floyd Patterson, Ken Norton, Joe Frazier, George Foreman, Ron Lyle, and Earnie Shavers.

Ali finished his career with back-to-back losses in the early 1980s to Larry Holmes and Trevor Berbick — fighters he'd likely have beaten with ease had he fought them in his prime.

Ali is the only three-time lineal heavyweight world champion, and held and retained the WBC, The Ring, and the WBA championship belts numerous times.

The WBC title he won after knocking out Foreman in the historic "Rumble in the Jungle" bout on October 30, 1974, in Zaire sold Sunday for $6.18 million.

Indianapolis Colts owner Jim Irsay secured the winning bid, Boxing Scene reported this week.

"Proud to be the steward," Irsay wrote on Twitter.

The NFL franchise owner also the belt would be included in The Jim Irsay Collection show at Chicago's Navy Pier on August 2.

It will also be displayed in Indianapolis September 9.

Irsay's memorabilia collection also includes other Ali-related artifacts, according to Boxing Scene, including the robe the fighter wore ahead of his rematch against Liston in 1965.