There are downsides to being a longtime action-movie hero, as Sylvester Stallone has found out: He’s had four back operations, two shoulder surgeries and a spinal fusion, that one after he fractured his neck filming “The Expendables.” Over the years, expectations of his assumed athletic prowess grew so high that he stopped wanting to play golf or basketball with anyone. When opinions about his acting abilities hit their nadir, around the time he won a Razzie for worst actor of the century in 2000, he half-agreed with his harshest detractors.

“When you become synonymous with blunt-force trauma,” Mr. Stallone, 69, said in an interview here, his basso profundo voice sounding like it was rising from the earth’s core, “you’re not really leaving anyone with thought-provoking aftershocks of your performance.”

All of which made an unexpected upside of devoting a career to playing he-men especially sweet. Mr. Stallone’s Oscar nomination, for his supporting performance in “Creed” — the seventh film in the “Rocky” franchise, which won him his last Oscar nominations four decades ago — has left him, by all outward showings, enormously grateful and glowingly proud, if slightly befuddled.

“For somewhat of a borderline misanthrope, this is incredible,” Mr. Stallone said. “It’s the pinnacle of my life, professionally. It’s so miraculous.”

Three and a half weeks earlier, he had collected a Golden Globe for his performance in “Creed,” a win that left him so dumbfounded that he failed to notice the standing ovation of the crowd. He had also failed, to his lasting dismay, to thank the film’s writer and director, Ryan Coogler, or his co-star Michael B. Jordan, which had prompted tut-tutting from Samuel L. Jackson, among many others, on Twitter.

“When Sam Jackson called me out on it, I totally agreed,” Mr. Stallone said. “Forgetting to thank the director? Believe me. That’s the last thing I would’ve done.”

If Mr. Coogler and Mr. Jordan were miffed, they hid it well. “I love the guy!” Mr. Jordan exclaimed at an after-party that night. Then he, Mr. Coogler and Mr. Coogler’s fiancée headed for the airport, and Mr. Stallone’s private plane, which spirited them across the Atlantic for the premiere of “Creed” in London. “Sly was cracking us up the whole flight man,” Mr. Coogler recalled. “It’ll go down in history, something to tell my grandkids.”

By week’s end, the awards news shifted to the homogeneity of the Oscar acting nominations, which all went to white actors. That Mr. Stallone received the lone nomination for “Creed,” a film written and directed by a black man and largely about black characters, only fueled the controversy, making Mr. Stallone’s joy over the recognition bittersweet.

“This guy here deserved it before I deserved it — this is his baby, and I just hung on for dear life,” Mr. Stallone said, referring to Mr. Coogler. “When he brought ‘Creed’ to life, he brought me to life.”

As talk of boycotting the ceremony circulated, Mr. Stallone said that he asked Mr. Coogler whether he should not attend the ceremony. (He recounted this story again at the Oscar nominees’ luncheon on Monday.) “I really wanted to get his opinion on what he thought my behavior should be,” Mr. Stallone said. “He said, ‘You should go, enjoy yourself and represent the film.’”

In a phone interview, Mr. Coogler fell silent when questions about the protest, #OscarsSoWhite, were posed, but said he was thrilled for Mr. Stallone. “Any good thing that comes to Sly, I smile ear to ear,” Mr. Coogler said. “The movie was such a family affair. Whenever anything comes for it, it feels like a piece for all of us.”

For this interview Mr. Stallone, sartorially impeccable, his face looking as hewn from granite as ever, went to the five-star Peninsula Hotel. The place was impeccable, and, after sitting down, Mr. Stallone, who comes across as self-aware, self-effacing and a little silly, slid a plate of macarons and petit fours across the coffee table. “I bought these for you,” he deadpanned. “Very sweet of me, I know.”

He had met Mr. Coogler, who he described as “a full-fledged genius, a savant,” three and a half years ago, before Mr. Coogler’s first feature, “Fruitvale Station,” came out.

The younger director came up with the idea for “Creed” when his own father, a devout “Rocky” fan, fell gravely ill (he has since recovered). Mr. Coogler wanted to tell the story of the illegitimate son of Rocky Balboa’s old boxing foe and friend, Apollo Creed. Set in present-day Philadelphia, the film would explore the city’s vibrant black culture through the eyes of Adonis Creed, who seeks out an aged and ailing Rocky to train him.

Despite landing a meeting with Mr. Stallone, Mr. Coogler did not think for a moment that the storied actor would agree to the film. So, en route to Mr. Stallone’s office, Mr. Coogler stopped at a Best Buy to get a Blu-ray of “Rocky II” for Mr. Stallone to sign. The movie was his dad’s favorite, and Mr. Coogler figured he would never see the star again.

Indeed, Mr. Stallone was wholly unconvinced, at least at first, having been happy with the series’ apparent final installment, “Rocky Balboa” (2006), which he starred in and directed, receiving respectable reviews. “A recipe for premier disaster,” was how Mr. Stallone viewed yet another Rocky film. Yet there was a confidence and buoyancy in Mr. Coogler that he intrinsically recognized. “He’s unspoiled, he’s unfettered with material success, and he’s hungry,” Mr. Stallone said. “He reminded me of some other brash young guy in 1975.”

One plot point (spoiler alert) in the “Creed” script that gave Mr. Stallone extreme pause, though, was Rocky’s cancer diagnosis. Mr. Stallone didn’t like it and didn’t think his audience would either, but Mr. Coogler would not budge. Mr. Stallone said he equivocated until his wife, Jennifer Flavin, called him out. “She said: ‘You’re afraid to do something you’ve never done before. That’s called being a coward,’” Mr. Stallone said, leaning back in his chair, and laughing. “She was right.”

To prepare for his role, Mr. Stallone hired a full-time acting coach, Ivana Chubbuck; his skill set, he said, “had basically atrophied.” When production began, he was still paralyzed by the devastation of losing his oldest son, Sage, who had a fatal heart attack in the summer of 2012 at 36. (Mr. Stallone has a second son, also from his first marriage, and three daughters with Ms. Flavin.)

He figured his grief would be off limits, but Ms. Chubbuck forced him to drill deep. “You just feel responsible,” he said, of Sage’s death. “That you weren’t there. Here you save all these fictitious people, and you can’t even save your son.” Once that floodgate opened, he said, his emotions streamed out, shifting both his performance, and his mourning. “It helped,” Mr. Stallone said. “I can talk about it now. There’s some solace in that.”

He has also found deep solace in the acclaim his performance drew from Hollywood’s establishment. Irwin Winkler, who has been producing films with Mr. Stallone from the first “Rocky” on, said seeing Tom Hanks and Steven Spielberg leaping to their feet to applaud Mr. Stallone’s Golden Globe win was especially gratifying.

“It would be a great moment for any actor, and certainly it was for Sly,” Mr. Winkler said. “I don’t think they gave him respect for the last 40 years.”

Looking back, Mr. Stallone said he’s not sure how much respect he deserved anyway. Appearing in action films became, for him, almost like an adrenaline addiction, he said, “an endurance contest that doesn’t challenge your soul, at all.”

The kudos he is receiving now makes him wish that he had pursued roles that involved showing vulnerability, which he did to glowing reviews in “Cop Land,” in 1997, and of course, in “Creed.”

“Now I look at it in the cold light of day, and they’re right, quite honestly,” he said, of his critics of yore. “I think the world could have lived without ‘The Expendables’ without spinning out of orbit. I really do.”