By Alex Fitzpatrick
March 8, 2017

The trajectory of Sir Patrick Stewart‘s acting career proves success doesn’t always follow a direct path.

After getting his start on stage with England’s Royal Shakespeare Company, Stewart went on to become an icon of American television and film, thanks to his roles as Star Trek’s diplomatic starship captain Jean-Luc Picard and the X-Men’s idealistic Professor Charles Xavier. Along the way, he has continued to work in theater, most recently starring alongside longtime friend Sir Ian McKellen in a London run of Harold Pinter’s No Man’s Land.

TIME recently spoke with the 76-year-old Stewart about his latest — and what he says will be his last — performance as Xavier in Logan. We also discussed his decision to seek American citizenship, his eternal optimism and the poop emoji.

TIME: When we first meet Charles Xavier in Logan, he’s worn down by time, he’s sick, he’s on some kind of medication. For anybody who has watched a loved one suffer from a mental illness, your performance came across as very true to that experience. What informed the way you brought that role, and particularly that scene, to life?

Stewart: As it happened, I had been doing research along these lines for some months for another role I was to play on stage. And in fact, I did play it for six months in London, and we wrapped the production just before Christmas [of 2016]. Everything that I learned and studied there proved to be helpful when I began thinking about Logan.

And I was very fortunate that about two years ago, not long before he died, the great psychologist and writer Oliver Sacks and I met, and we talked about some of the elements of the other role that I was pursuing. He was tremendously helpful. We actually ran some scenes for him, and his comment was, “Well, I see these people in my clinic every day.”

That was so helpful in the pursuit of trying to bring an absolute reality to a very, very painful, and at times tragic condition. Which is where we find Charles. Confused, disturbed, fragile, unstable, angry. And, as we learn pretty quickly, potentially pretty dangerous, because the power of this mind, which we have seen over the years in the X-Men movies, his powerful of control and investigation has now turned against him, or rather turned against society, because he no longer has control over it. And the only means by which he can be controlled is by the illegally-bought medications that Logan picks up. Which is keeping Charles not only alive, but safe, too. Because without his injections, and his tranquilizers, he is going to be a danger to himself and everyone and everything around him.

MORE How Logan Fits Into the X-Men Timeline(s)

TIME: This is a character who’s usually in control. He’s in a leadership role and he has the respect of those around him. But here’s a very different version of that character. How challenging was it as an actor to switch how that character is being portrayed?

Stewart: Well, I never see these things as challenges. Because that implies there is some difficulty to be overcome—there’s a hurdle that you have to in some way get over. I don’t feel that way about my work, or the kind of work that I always look for.

I began as an actor working in weekly rep in the provinces of England, and what that means is, that you do a whole brand new play every Monday night. And on Tuesday, you rehearse the next one, until Saturday and you put that on. And in that time—I was 18 then—you play a variety of roles. I enjoyed one week being an 80-year-old retainer in a role which was played by Ernest Thesiger when he was in his late 80s. Or, I’d find myself as a teenage young man dating a debutant. These were all plays that I did during that first year or so of my career. And I loved shifting from character to character, type to type, emotion to emotion.

So in a way, being in Logan is something I’ve been preparing for for a long time—17 years you might say, from the first time I wheeled my chair onto the set in the very first movie. And the opportunity to take a calm, composed, intellectual, compassionate, loving, non-violent man like Charles Xavier, and transform him into this crazy individual we meet in Logan, was just exciting, because I wanted to have all of the elements of the old Charles Xavier there, but now added to them was this instability, vulnerability, almost childish new development in his consciousness. It was, for me, one of the most invigorating parts of the two months that I spent working on this—exploring a Charles damaged, rather than a Charles in super-control as he always was.

TIME: X-Men stories have long been political allegories about exclusion, othering, even genocide. Logan touches on some of these issues, but the story ultimately comes across as more personal than political. Given the political climate right now, do you think the story would’ve been more effective if it was more focused on issues like that?

Stewart: I don’t. I think that the writers and the producers and particularly James Mangold, our director, had a script in mind which was exactly the script that, with Hugh [Jackman]’s massive support, and the support of the studio, and when I came in two years ago also my enthusiasm for it, is exactly what they had dreamt of. Which is to create a movie that still contained historic superheroes, but in which their humanity, both in terms of their vulnerability, their neediness, their longing for something different and better, became paramount. And that’s what they’ve produced in this screenplay.

TIME: You recently said you’re going to apply for American citizenship. Can you tell me why?

Stewart: I’ve been a resident alien, which is always good for a laugh [pauses for laugh], for almost 30 years. The United States has given me an extraordinary career. And I do have to say the United States and Hollywood, because until 1987, if you didn’t go to the Royal Shakespeare Company or occasionally watch classic revivals on BBC television, you would have never have heard of my name. All that changed in 1987 [when Star Trek: The Next Generation first aired], and two years later I applied for and received my green card, which I’ve held on to ever since.

I [have] lived in this country for 17 years. It was my home. And my indebtedness to this country, and to Americans, who have come to be such a powerful influence in my life—I mean, I married one, my son did the same. During the last few months of anxiety about the situation in Washington, I found myself increasingly reflecting on my inability to play a part in what was going on.

I’ve been in politics all my life. In 1945, I committed my first act of civil disobedience during the election campaign for the first post-World War II general election, when the Labour Party, to everyone’s amazement, ousted the Conservatives. I refused to obey the instructions of a policeman, and as a result, almost got a belt around the ear, because those were the days when policemen could hit children and nobody cared, they thought it was probably good for them.

So I’ve been an activist all my life. And always a liberal activist, for the simple reason that it is on the liberal left that you find the true recognition for the need for fairness in society. I’m not saying equality, because that you can never achieve, because equality is based on such complex criteria. But fairness is another issue.

In 1990, I campaigned modestly for Al Gore. And I do mean modestly, because as a non-citizen, I knew there would come a point when my campaigning would become counter-productive. Well, at my great age now, I think it’s time to change all of that. So that’s why I made that remark. I was astonished by how much everybody paid attention to it. I would not have thought, in terms of media interest, it would be that important.

TIME: Science fiction has a habit of portraying the world as bleak and hopeless. But the two major sci-fi characters you’ve played, Charles Xavier and Jean-Luc Picard, both believe in a better future for humanity, or mutants. Do you think we’re on the right path? Are you also optimistic about humanity’s future?

Stewart: I always have been. Always. Even at the most dismaying of times.

I grew up in a quite poor working class home with working class parents. My grandparents were the same, my great-grandmother could not write her name, she simply made a cross on her wedding certificate. I’ve been a witness to unfairness in society all my life. To the conditions under which my mother worked all her life, working in an industrial weaving shed in the north of England. And it has been this feature of unfairness that has motivated me in all of my political thinking.

So, I think you can only do that if you are fundamentally optimistic that the world can be changed. And I am. Because the alternative is a kind of despair that will do nobody any good. I know it feels like two steps forward and one step back, but we are making progress. In my lifetime, I have lived through one World War, I have lived through the end of Apartheid in South Africa, the pulling down of the Berlin Wall. I have experienced what I never thought I would have experienced, which is a pretty workable peace in Northern Ireland, and I experienced a unified Europe—until the Conservative government got its hands on the idea that in order to appease a few back-benchers they would hold a referendum, what a disastrous idea.

You get the message, I’m an optimistic person. Which is why playing Charles Xavier and Jean-Luc Picard, were so satisfying to me. Because both of them were optimists.

TIME: A few weeks ago, you seemed to be on the fence about letting the Xavier character go. But now you’ve said you’re ready to move on. What caused the change of heart?

Stewart: It was only a couple of weeks ago. Hugh I knew, he was on record as saying this would be his last movie as Wolverine. And I hadn’t even thought about that from my point of view.

We were in Berlin, at the film festival, and I was sitting next to Hugh. We got into the last five minutes of the movie, and I found myself subject to waves of emotion, although I’d seen the movie once before, and I was not involved in the shooting of those last scenes. But I found it so intensely moving and affecting, that I could feel my eyes welling up with tears. And then, Hugh reached over and took my hand in his and squeezed it and looked over, and then with his other hand, I saw him wipe his cheek. And I thought, well, if Hugh Jackman can wipe away a tear at the Berlin Film Festival, then so can I.

MORE How Logan’s Young Heroine Could Save the X-Men Franchise

And then the movie ended, and while the credits rolled, I realized this is so beautiful an ending. An ending I am so moved by, in which Charles is in absentia included, that maybe it’s my time, too. By the time I got up on stage, I was content in myself that I had done and said all the things so far as X-Men and Wolverine were concerned that I needed to do to reinforce the point of the whole series. Which, if you remember the first X-Men movie, directed by Bryan Singer, began at the gates of a concentration camp. There has been that political, societal element with these movies from the very beginning. And that gave many of us involved with them a great deal of satisfaction.

TIME: Your next big project is The Emoji Movie, and you’re playing Poop. What got you interested in that role, what are you excited about doing with that?

Stewart: Well, frankly, two things. Just the sheer outrageousness of it. And the fact that I know it would be regarded very highly by my grandchildren. I remember my grandson saying, “cool, granddaddy’s playing poop!” So like I said at the beginning about diversity, it seems very appropriate that the next thing I should move on to should be a pile of shit—in the best possible sense.

This conversation has been lightly edited for length and clarity.

Write to Alex Fitzpatrick at alex.fitzpatrick@time.com.

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