The autographed photo hung in my bedroom for much of my childhood. It was given to me when I was 6 years old and it was signed by Muhammad Ali.

The photograph, like my baseball cards and comic books, is gone now, but I will never forget the man in the picture. Ali was in a fighting stance. He was sleek and strong. His expression was serious and his eyes were focused.

When I was 10, I watched Ali and Joe Frazier in “The Thrilla in Manila.” It was the final, brutal chapter in a three-fight trilogy. My father, Bobby Cassidy Sr., then a light heavyweight contender, had just won a 10-round decision at Nassau Coliseum. After the live boxing card, they dropped movie screens from the rafters and broadcast the Ali-Frazier fight via closed- circuit TV from the Philippines.

My brother Chris and I were too preoccupied with our father, our own champ, to fully understand the magnitude of Ali-Frazier III. The only thing my father said — ordered, actually — was “pay attention to this.”

There were certain images from that night I will never forget. The first was the vitality of Ali. He was so vibrant. He pointed and shouted during the prefight introductions. He picked up a large winner’s trophy that sat in the center of the ring and carried it to his corner before even throwing a punch. When the crowd in the Philippines booed, Ali pretended to cry. The crowd at the Coliseum also booed.

When it did come time to throw punches, Ali and Frazier didn’t disappoint. No one was booing. My father, at various points during the fight, actually stood on his chair for a better view.

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They say the best fights are made between great fighters who are just past their primes. The skills and reflexes are slightly faded, but the courage and determination never diminish. The result is a bout in which a lot of punches land. This was Ali and Frazier on Sept. 30, 1975. Two ancient warriors, desperately trying one last time to conquer the other.

So much of the action in the ring has been reinforced in my mind by repeated viewings on ESPN Classic. Ali won the early rounds, peppering Frazier with left-right combinations, but by the eighth round, the fight had turned. It was Frazier, wading forward, slamming that wrecking-ball left hook into Ali’s midsection. My father spent more time on top of his chair as the crowd noise at the Coliseum rose around us.

The fight turned again in Round 12, with Ali ripping more left-right combinations. Frazier was bleeding from the mouth and his eyes were beginning to swell. In the 13th, a right from Ali sent Frazier’s mouthpiece skidding across the ring. In the 14th, Frazier, his eyes slits, was no longer bobbing and weaving. He was standing straight up, accepting all of Ali’s punishment. When Frazier wobbled back to the corner, his trainer, Eddie Futch, had seen enough and stopped the fight.

“It was like death,” Ali would say later of the fight. “The closest thing to dying that I know of.”

There may be athletes who have given as much to their sport, but no one will ever give more of themselves than Ali and Frazier did that night.

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As a reporter, I covered Ali at numerous boxing functions through the 1990s. The hands that delivered those rapid combinations quivered. The voice that shouted “I am the greatest” was muted. Ali had been diagnosed with Parkinson’s syndrome in 1984.

Ali often would do appearances with rivals Frazier and Larry Holmes. Unable to raise his voice above the other fighters, the man who always dominated a news conference could only sit back and listen as Frazier and Holmes beat him to the punchlines. It was hard not to feel for the man.

The Parkinson’s worsened over the years, and Ali’s public appearances became far less frequent. It was easier for me to remember the man in the photograph.

My father fought in person with Ali twice — when Ali beat Frazier in the second fight at Madison Square Garden and when Ali beat Chuck Wepner at Richfield Coliseum in Cleveland. But it was training at the 5th Street Gym in Miami where my father interacted with Ali.

They were acquaintances — a nod hello, a quick handshake. They’d walk the same circles when the bell rang inside the gym, sucking the hot, humid air into their lungs before the bell summoned them back to their respective heavy bags.

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In January 1971, my father fought former welterweight champ Luis Rodriguez in Miami. Rodriguez and Ali were trained by Angelo Dundee and they too spent many hot afternoons together at that gym. It often has been said that Rodriguez’s flashy style influenced the young Ali.

My father dropped Rodriguez in the first round but lost a close split decision. The fight was in Rodriguez’s backyard and close fights always seemed to go to the hometown fighter back then. Still, my father was devastated.

He was sitting in his dressing room, staring at the floor, when Ali walked in.

“Hang in there, kid. You won that fight,” Ali told my father. “You’ll be a champ someday.”

Ali then offered to autograph some photos for my father to bring home to his children.

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The inscription read, “Dear Robbie, Your Daddy is the Greatest — Muhammad Ali.”

Ali was a lot of things to a lot of people. In that small moment, to my dad, he was a friend. And to me, on my bedroom wall, he was a hero.