Disturbingly stoic, violent and seeking absolution he’s not sure he needs, the mob killer Frank Sheeran allowed Robert De Niro to deliver a majestic, subtle performance in “The Irishman” that has the feel of a crowning achievement — and for reasons that go beyond the screen. Based on Sheeran’s memoir, “I Heard You Paint Houses,” the film is haunted by the cinematic moments that De Niro, the director Martin Scorsese and the co-stars Al Pacino and Joe Pesci have made in so many movies about hard men with hollowed hearts. “The fact that me, Joe and Al were doing this film is something in and of itself,” said the halting, taciturn De Niro, who also played a key role in this fall’s controversial, Scorsese-indebted “Joker.” “Marty directing it says something. It all sets a tone. The audience’s perception of each character, us actors being together and what the story is — the film is all those things.” It’s also a reminder, as if we needed one, of the brutal and beautifully unsentimental revelations that only a peak De Niro performance can provide.

In getting ready to play Frank Sheeran, you dug deep into the source material, and you also spoke with people who knew the guy. But I’m curious how your thinking about preparation has changed over the years. You’ve said in the past that you don’t kill yourself with it the way you did when you were younger. What I meant was that maybe it’s not as necessary to be so obsessed. It’s better at times to be relaxed. Do all the preparation before, and then just do the scene, and don’t be anxious about it or amped up about what it is. Getting so concerned about an emotional scene — you can kind of short-circuit whatever’s going to come.

Was there a performance that led to that realization? No. I just felt that a real emotional situation in life comes due to the circumstances around you. If you prepare too much — you know the joke about the actor who couldn’t remember any lines?

No, I don’t know it. This actor can’t remember lines, so he can’t get a job. A director he knows runs into him at the gas station where he’s working. The director says: “I have a play that in the third act, what you do is go and say, ‘Hark, I hear the cannons roar.’ Can I count on you to do that?” The actor says he’ll do it. He goes and rehearses, rehearses, rehearses. “Hark, I hear the cannons roar. Hark, I hear the cannons roar.” On the day of the play, the third act comes, and the actor runs out onstage. Boom! The cannon goes boom, and the actor goes, “What the [expletive] was that?!” The point is, you don’t want to lose spontaneity.

Jack Davison for The New York Times

Earlier in your career, there was a lot of attention paid to how you changed your body for your work in, to pick just the most famous example, “Raging Bull.” In “The Irishman,” your body changed too, but the changes were made digitally, to allow you to look younger. How did it affect the performance not to be able to feel those changes physically? Well, it’s harder to act younger than it is the other way round. We had a guy named Gary Tacon who was a movement coach. He would tap you and say, “You’re 39 in this scene.” In one case, I was walking down the stairs a little more carefully than my character would’ve, and Gary showed me that you kind of fall down the stairs when you’re younger. So I did that. I did it well. Marty cut it out because he didn’t need it. But it was that kind of stuff. You have to be aware of having a certain spryness.

And you felt that you could credibly achieve that? I felt that, but even so, some people felt it was not — they weren’t criticizing it. They were saying they could see my real age. O.K., fine, that’s interesting. I should’ve taken steroids or something. They’ll youth-ify you or de-age you or whatever, but you still can’t look like you’re crotchety. It’s a good thing. You know, Marty would see, and I saw it, too, that there would be an expression in my eyes during a scene, but after they youth-ified me, my eyes had a different emotional expression. Marty was concerned about that. I had the right emotional intention, the right attitude, but when that de-aging came, the expression in the eye changed. So they had to figure out a way to make sure that after I was youth-ified it would not alter the intention of the scene as we acted it. It was an interesting problem.

You could think about a character like Frank — or a lot of people you’ve played — as fundamentally inhumane as written on the page. But you have a way of infusing all these vicious characters with something approaching soul. Are there keys to doing that? The rule in acting is you never make a judgment about your character. The characters have their reasons, and you understand them. You’re trying to look at their point of view. I mean, in “The Irishman,” Frank has a problem with his daughter. He has problems that anybody can relate to. I never thought of him as being amoral or immoral. He lives in a world where the penalties are harsh if you don’t do what you’re supposed to do. He says he’s going to do something, he does it. I don’t like to go to Trump, but he is a person who, to me, has no morals, no ethics, no sense of right and wrong, is a dirty player.

Could you find your way into the character of President Trump? I wouldn’t want to play him. He’s such an awful person. There’s nothing redeemable about him, and I never say that about any character.

You found redemptive qualities in Travis Bickle, and you’re saying you couldn’t do the same if you were playing President Trump? I can’t compare. There’s not one moment that Trump said: “I’m sorry. I realize I’ve done something that I shouldn’t have done.” He has not one speck of redeemability in him. He’s not owed one speck of redeemability.

People have argued that some of Trump’s rhetoric has emboldened others to make threats or enact violence. Those arguments are not a world away from ones that people made about Travis Bickle or “Joker.” Do you think those arguments hold water? They might, but Trump has people who follow him who are crazy and want to do crazy things. What we’re doing in film, it’s like a dream. We know it’s not real. There are people who will take anything to be real and that we have no control over. The president is supposed to set an example of trying to do the right thing. Not be a nasty little bitch. Because that’s what he is. He’s a petulant little punk. There’s not one thing that I see in him or his family, not any redeeming qualities. They’re out on the take. It’s like a gangster family.

To shift subjects a bit, what about if somebody were looking to play you? Would you be willing to talk with them and help out with their preparation? That’s a good question. I don’t know. I’ve always experienced that people are open because they want you to get it right. They want to give you information. With “Raging Bull,” Jake LaMotta was great with me and Marty. He was happy that we were making a movie about him. Certain things, maybe it was our interpretation. That’s the same with Frank Sheeran and “The Irishman.” In acting they say: Make it your own. Personalize it. It’s the same thing with these stories. There has to be some — I don’t like to say poetic license, because that has a negative connotation when it shouldn’t — but it’s a way of expressing how you see it. It doesn’t mean it’s right. But it’s how you see yourself.

What did you see in yourself that you put into Frank Sheeran? Aha! That is the question.

Jack Davison for The New York Times

What’s the answer? That is the question, but the answer is personal. I mean, when I talked to Marty about certain things about the film — sometimes he’s like a priest. We talk, and I have to be honest with him in order to get stuff in the film that we need to say. But it’s personal stuff that I would express through the character. It’s not stuff I’d tell other people.

I know you’ve thought about one day sitting down and watching all your own movies. What would you hope to see? I would probably be apprehensive, because I’m critical about what I did. But the other thing is what I could learn if I looked at all my stuff and got an idea of what I’ve done, what the pattern is. Because I’d like to do something that’s really different from what I’ve done or been known to do.

If you watched all your performances, do you think you’d feel any pride? I have reasons that I look at my stuff and I’m not happy. Other people look at my stuff and say they don’t even know what I’m talking about. I don’t know. It’s not for me to say.

David Marchese is a staff writer for The New York Times Magazine and the Talk columnist. Recently he interviewed Pete Townshend on rock’s legacy, Patti LuPone about being bullied on Broadway and Whoopi Goldberg about creative fulfillment. Jack Davison is a British photographer. His work has been featured in British Vogue, Modern Weekly China and recently in the magazine with a cover photograph of Glenda Jackson. His first book, “Photographs,” was published by Loose Joints earlier this year.

Stylist: Brian Molloy. Grooming: Lynda Eichner. Clothing: Charvet.

This interview has been edited and condensed from two conversations.