A sports icon in his own right, NFL great Jim Brown says Muhammad Ali stands alone in his ability to affect social change.
"He was able to use the spotlight like nobody else in history," Brown said.
The Hall of Fame running back became close friends in the 1960s, bonding with the heavyweight champion over their shared beliefs on equal rights and justice. Brown stood alongside Ali when he challenged being drafted for the Vietnam War.
"He represented what a man should be in an America that's free because he made people accept him as a man, as an equal and he was not afraid to represent himself in that way," Brown said. "That's what I loved about him."
And while Brown admired Ali's seriousness on important matters, he also enjoyed the boxer's playful side.
Brown chuckled as he recalled Ali visiting his home in California and giving him a pair of boxing gloves as a gift. It wasn't long before Ali wanted to spar with Brown, who was then given a lesson in the sweet science.
"He just played with me and tapped me in the face and tapped me on the head and showed me all the tricks of the trade," Brown said. "We had a great laugh because he was also a great comedian."
Spectators at the French Open men's final, many of them standing, have paid tribute to Ali with a sustained bout of applause before the title match between Novak Djokovic and Andy Murray. A photo of Ali, who died Friday at age 74, was shown on the jumbo screen overlooking the Court Philippe Chatrier.
Djokovic told a TV interviewer that he is feeling "a lot of emotion" before the "very important match."
Murray said he's "looking forward to it" because "these are matches you play for."
Tennis great Billie Jean King remembered Ali as fun to be around. She witnessed the Muhammad Ali-Joe Frazier fight at Madison Square Garden in 1971 and saw him there again in 1999 for Sports Illustrated's celebration of the top athletes of the 20th Century.
"He always whispered in my ear, 'Billie Jean King, you are the Queen,'" she said.
King won 12 Grand Slam singles titles during her career in the 1960s and 70s, while Ali was rising to stardom in his sport. King says Ali "talked the talk and walked the walk."
Jack Nicklaus has only photos of his family and U.S. presidents hanging on the walls of his office at home. The one exception is Ali.
He met Ali for the first time in 1996 at the PGA Championship in Louisville, and Nicklaus said it's one of his favorite pictures.
"I had my hands thrown up, sort of, 'Don't hit me, please,'" Nicklaus said Sunday. "I've always liked that picture. It was my first meeting of Ali. We actually touched base quite a few times after that and I got to know him a little bit. Obviously, he didn't communicate all that well. But he meant an awful lot to the sport of boxing and the sporting world."