Roughly 30 years ago when boxing was in its golden age, Ray “Boom Boom” Mancini was at the top of his game. As the lightweight champion of the world, the fearless puncher from hard-scrabble Youngstown, Ohio, was on the verge of becoming not just the most popular figure in his sport but also an international sensation with a story gift-wrapped for Hollywood.

Mancini had taken his nickame from his father, Lenny, himself a professional fighter who took on shrapnel in World War II and thus was unable to continue his career in the ring. So the son picked up the mantle and dedicated his World Boxing Association championship to his father, calling it his greatest day.

Then came a fight against Duk Koo Kim in November 1982 that changed not only the lives of the principles but also those closest to them and the landscape of the sport itself.

In the 14th round, Mancini landed several shots to Kim’s head, and the South Korean went down before lifting one arm over the other to get back on his feet. Referee Richard Green stopped the fight, but Kim lost consciousness soon thereafter and died four days later from a blood clot in his brain.

Kim’s fiancée had been pregnant with the couple’s son, and as close as Mancini was to his father, the guilt at times was too overwhelming, and by his own admission, he was never the same fighter again.

The documentary “The Good Son” based on the same-titled book by bestselling author Mark Kriegel examines that seminal time in Mancini’s life but also goes into detail about the fighter’s relationship with his father, his home town and how he since has dealt with the tragedy.

“We’re connected forever obviously,” Mancini said before a screening of the film Thursday night at the home of Ted Leonsis, majority owner of the Washington Capitals, Wizards and Mystics. “I’m connected with the Korean people. It’s like Americans who remember where they were when Kennedy was shot.”

The producers of the “The Good Son” are Chris Tavlarides and Jimmy Lynn. Both are natives of the District and attended the screening along with Mancini and a host of other area A-listers, including Nationals owner Mark Lerner and Kevin Plank, founder of Under Armour.

Among the most poignant moments in the movies comes when Mancini and his family meet Kim’s son, Jiwan, and mother for the first time. The exchange includes Jiwan telling Mancini he shouldn’t live the guilt because the death of his father wasn’t entirely his fault.

In another especially powerful conversation, Mancini tells Jiwan he never thought about quitting in the ring, except in the late rounds against his father. The fight was supposed to be little more than an exhibition for the heavily favored Mancini, who recalled landing blow after blow but never saw Kim retreat.

Kim instead delivered flurries near the end of rounds just when it seemed he was ready to hit the canvas.

“This for us hopefully is our altruistic way of giving Ray closure,” said Talvarides, who called the project fulfillment of a lifelong dream. “He deserves it.”