If you were standing 15 years ago in front of Louisville’s Broadway Cinemas, in which Will Smith was playing “Ali,” and looked either way down the wide avenue, a story of a different part of Muhammad Ali’s life comes into view. It’s the story of Cassius Clay.

If you turn right, you’re headed toward the one-story cottage on Grand Avenue where he grew up. If you turn left, you’re headed toward the building on South Fourth Street downtown that housed the basement gym where he began to box. You can walk down South Fourth and find a 12-year-old Cassius sitting on the steps of the Columbia Auditorium, crying and angry. Somebody had stolen his new Schwinn.

A man told the boy he could complain to a policeman who happened to be in the building’s basement, where he operated a boxing gym in his spare time. “If I find the guy who took my bike,” Cassius told the late Joe Martin, the part-time trainer, “I’m gonna whup him.”

As Martin’s son, Joe Jr., recalled, his father asked, “Do you know how to fight? You should know how to fight if you’re going to whup somebody.”

Cassius had never thought of boxing until then.

You could almost describe the meeting of the boy and the trainer as miraculous. “Had they not met,” Martin Jr. said, “there might not have been Muhammad Ali.”

The next night the kid came back to the gym — and night after night he kept coming back.

Soon, people began to hear about a talkative youngster who was calling himself “the greatest.”

The late boxer Jimmy Ellis, also a son of Louisville, remembered watching Ali on a small screen. It was his family’s television set and the picture was black and white. It was a Saturday evening and a local station was airing Martin’s weekly amateur card known as “Tomorrow’s Champions.” Cassius Clay, the up-and-comer, was fighting Ellis’s friend Donnie Hall. The next time he saw Hall, Ellis said to him, “How’d you let that chump beat you, man?”

Hall got Ellis to the gym, and when he was ready, Ali beat him, too. They fought again, and this time Ellis won — three two-minute rounds with oversize gloves. After that, they settled on being friends.

Washington Post obituary writer Matt Schudel, who co-authored "Muhammad Ali: The Birth of a Legend, Miami, 1961-1964," discusses the boxing legend's legacy outside of the ring. (Thomas Johnson/The Washington Post)

Ellis was a little older and had a car and would give Cassius rides home, all the way out Broadway to Grand, or until Cassius might say, “Hey, let me out here.” He would jump out of the car and run the rest of the way home, punching the air in stride.

He charmed a nun who ran the library at what is now Spalding University, across the street from where the gym was. Sister James Ellen Huff of the Sisters of Charity of Nazareth gave him a job dusting so he could make a little money. She said he liked his “zest.” Sometimes she would return from dinner with a snack for him before he went to train. Once she returned and found him asleep on a long library table. After the world came to know him, she put a sign over the table that read, “Cassius Slept Here.”

“Dad used to compare him to Ted Williams because he had such great hand-eye coordination,” Joe Martin Jr. said. By 1960, everybody who knew Clay realized he had a chance to make the Olympics and win a gold medal. But he was afraid to fly. The Olympic trials were in San Francisco.

“Before he took that plane, he went down to the surplus store and bought a parachute. It was a rough flight, so rough that Dad got knocked out of his seat. Cassius was on his knees in the aisle, praying, with the parachute on his back.” He hitchhiked home.

One day a short time later, the trainer and Cassius sat in a park a few blocks from the gym and talked for about an hour. “Dad told him he simply had to fly to Rome or he could never win a medal and maybe never become heavyweight champion of the world,” Martin Jr. said. “Cassius wanted to take a boat.”

Ellis passed time at a senior citizens day-care center where he helps out, and recalled a time when he, Jimmy Ellis, was the heavyweight champion. That came after Ali had been stripped of the title and banned from boxing — but Ellis’s reign didn’t last long. He was better known as Ali’s sparring partner, and when they met later in the ring as professionals, Ali won.

But as Ellis paused and looked back, it wasn’t Ali on the screen he was seeing but rather the Cassius Clay he knew when they were youths. “He could move, do things in the ring just like he could when everybody got to know him. I fell in with him. He was fun to be around. The one thing we talked about was boxing. We’d get to sit down and get something to eat and we’d be talking about who was going to be champion, who could beat who. He’d say, ‘Ain’t nobody can beat me.’ And hardly anybody at the time could beat him. He could always box.”

William Gildea was a sports reporter and columnist at The Post from 1965 to 2005.