Naazim Richardson, a prominent Philadelphia boxing trainer for Bernard Hopkins and many other notable fighters, has died after a long illness.

No cause of death was released, but Mr. Richardson’s health had been in decline after suffering a stroke in 2007.

Along with Hopkins, Mr. Richardson, 55, trained Shane Mosley, Karl Dargan, and Steve Cunningham, among others. He was Hopkins’ lead trainer when he upset light-heavyweight champion Antonio Tarver in 2006, and he helped Cunningham become a cruiserweight champion.

In an Inquirer story in 2014, Hopkins said he and Mr. Richardson connected well because both managed to rise from difficult upbringings.

“We feed off each other’s adversity,” Hopkins said in 2014. “Everyone has a story that could have ended their lives or stopped their careers. But somehow we found a way to not fall victim to those challenges. It’s good to know that he’s a fighter, not a quitter.”

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Mr. Richardson’s most notable moment came in 2009 before Mosley’s fight with Antonio Margarito. Mr. Richardson was watching Margarito wrap his hands when he picked up a cushion off the table and noticed how hard it was. It was discovered that Margarito had wet pads in his wrapping, and the California State Athletic Commission revoked Margarito’s license for one year.

Stephen Fulton Jr. was one of the Philly fighters whom Richardson helped. He stood in Fulton’s corner for some of his biggest fights and helped train him. On Aug. 1, Fulton will be fighting for the WBO junior-featherweight world championship.

“I was the last fighter whose corner he was in that he coached,” Fulton said. “He taught me a lot, and he also taught my coach, Hamza Muhammad, a lot and helped us along the way.”

Trainer and fellow boxing coach Shar’ron Baker was often by Richardson’s side. She helped him coach Cunningham and Dargan, along with many other fighters. She considers seeing Cunningham fight on the Floyd Mayweather-Conor McGregor undercard in 2017 one of her greatest boxing experiences, and that was a moment she shared with Richardson.

“Naazim was my brother, my mentor, my friend. We worked together over 15 years and he never called me his assistant but rather his partner,” Baker wrote in a text. “One of the greatest boxing minds and just a great guy all around. He will truly be missed by all. He meant the world to me.”

Mr. Richardson’s two sons, Tiger and Rock Allen, were professional boxers and amateur standouts.

Mr. Richardson spent most of his childhood in the Germantown section of Philly before becoming a trainer. In the community, he often gave kids free boxing lessons.

He’ll be remembered as one of the best trainers the area has ever seen. Boxing greats have taken to social media to pay their respects.

Mr. Richardson is survived by sons Rock and Tiger Allen and Bear Richardson among others. Funeral arrangements have not been announced at this time.