Sitting through the premiere of his latest film, “St. Vincent,” Bill Murray was unexpectedly moved.

“I thought, ‘Well, I better not be crying when the lights come up,’” Murray recalled in an interview shortly after the film’s Toronto Film Festival debut. “That would be bad for my image.”

His image — deadpan and dry, but always game, ever-adventurous — has swelled over the years. Who by now doesn’t know that directors seeking his services must leave a message on an 800 number that he checks infrequently, and pray for a response? Or that he signed up for “Garfield” because he thought the Coen brothers were involved, mistaking the name of screenwriter Joel Cohen. And who hasn’t heard of (or better yet experienced first-hand) some serendipitous encounter with Murray — a drop in at a bachelor party, a cameo at karaoke?

These are the stories that have built the Myth of Bill, one that’s so satisfying because of its authenticity. He grants that many are after “the Bill Murray experience,” as he calls it, something he doesn’t mind except for the autograph hounds outside his hotel that make him want to “go through a sheep dip,” he says.

For an actor that has worked irregularly, “St. Vincent,” which opens Oct. 17 in Atlanta (date subject to change), is his most challenging part in years. It’s a technically demanding role that includes a coarse Brooklyn accent and portraying the aftermath of a stroke. He gruffly but tenderly mentors a shy boy next door (Jaeden Lieberher, whose mother is played by Melissa McCarthy), teaching him an upper-cut, not to mention how to play the trifecta.

The film caps a flurry of activity for Murray: a month in Hawaii for a Cameron Crowe movie and a Barry Levinson film that he says “could be mind-boggling.” While popping jelly beans in a hotel room, Murray reflected on his newfound ambition, his Oscar hopes and how he stays relaxed.

Q: This might be your biggest part since Jim Jarmusch’s “Broken Flowers” in 2005.

A: It is ambitious and it is larger. I’ve just been taking the jobs I like. I haven’t had any kind of a plan, really. It really was a big, leading part. I thought to myself, “God, I haven’t had to be the leading part in a while.”

Q: Playing a stroke victim rehabbing with slurred speech would scare me if I was an actor.

A: Scared me, too. I hate that not-having-your-faculties acting. That’s like acting school. I don’t want to go to acting school, ever. That was like doing ordinals or cleaning paint with a small razor blade. It’s the worst kind of work. Deep cleaning. And, yet, I didn’t have a stroke. Life could be worse. I’m not complaining. I could be the guy with the stroke.

Q: This film could have easily slid into sentimentality, something you’ve made a career out of avoiding.

A: Sentimentality to me is a symbol that we’ve left the planet. OK, bye-bye. Let me know when you come back because you’re no longer here. You just left. It reminds of being at a funeral, like my dad dies and the grief is just overpowering. And all anyone can say to you is, “Well, he’s probably up there in heaven, bowling with Uncle George.” It’s like, “Yeah, that’s probably it. He’s up there bowling with Uncle George.” He’s dead. He’s gone. What am I going to do? Talk to ME. Don’t make up your own dreamscape. Stay here with me, will you? Don’t go away.

Q: You’ve long avoided separating yourself from the public.

A: Most people are fine. The percentages are the same as they are in your life, the people you meet. The range of experience is the same for all of us, I think. I just have a lot more of them. A lot more of them.

Q: Why don’t you surround yourself with the kind of representatives most celebrities have?

A: From the first time I was ever given a bodyguard, I thought, “Oh my God, I’m going to be assassinated.” It made me think I was going to be shot. So I never liked it. I never liked the sensation of it.

Q: Harvey Weinstein will surely push you for an Academy Award nomination for this.

A: Oh, God, yeah. That’s what Harvey does. He’s not going to like me, but I’m just not going to get on the pony and ride from town to town, I don’t think. I hope not. Movies are magic, or they’re supposed to be something like it. Leave it alone. If you’re telling people how it works, you’re a jerk. You’re a loser that doesn’t know how to do it. But that running after prizes stuff, I was involved in that once before. It’s like a low-grade virus. It’s an infection when you really campaign for it. But it’s fun to win the prize because you get the chance to get up on stage and be funny.

Q: You seem to still enjoy that, like at the Q&A following the festival’s screening of “Ghostbusters.”

A: Like shooting fish in a barrel. You can do things with a few hundred people. You can really mess around. You can shock a lot of people at once. You have an incredible liberty to avoid everything that’s expected of a man at a microphone.

Q: You spoke then about the importance of staying relaxed.

A: You’re unconscious most of the time. Not out cold, but you’re unconscious. Lights on, nobody home. If you come back, “Oh, there I am again.” All of a sudden, you’re looking at yourself, like, “Where am I now? What was I thinking? What am I feeling? What’s my body doing?” Usually, I have a pang of remorse or a reminding, like, “Oh, here I am again. How was it I wanted to be living?”

Q: So it doesn’t always come naturally?

A: (Murray speaks at length about breathing deeply and relaxing tension in your body.) Then you can almost perceive a sort of connectedness between the parts in you. You’re not taut anymore. You’re free. You’re available for the next thing that’s there. And in the meantime, rather than try to think what that’s going to be, you can just receive something, like grace.

Q: Are you doing a good job of that?

A: Only when I remember. I’ve actually started saying, “I’m not a worrier.” People say, “Don’t worry about …” And I say, “I’m not a worrier.” I’ve found it to be extremely helpful. It helps things in some kind of psychological bag that you’re throwing me. Don’t throw me a coiled up rope. Give it to me straight.