When actor Christopher Lloyd attends fan-fueled events, people request the simplest thing: They just want to hear him say "Great Scott!" in person.

Lloyd has more than 200 on-screen credits to his name, but for so many, he'll always be the wildly coiffed, catchphrase-ready Doc Brown from the Back to the Future trilogy.

Lloyd is coming to the Keswick Theatre on Saturday to host a screening of Back to the Future, the 1985 film where his character leads Marty McFly (Michael J. Fox) back to 1955 with the help of a souped-up DeLorean.

He will, of course, be happy to say, "Great Scott!"

Why do you think people love these movies so much?

I meet a lot of people who saw the movie when they were kids and they were impassioned by it, and they show it to their five-, six-, 10-year-olds, so it keeps going. It's a family film, it's not just for adults or just for kids.

There's this whole idea of time travel that we all think about at one time, or to see the future. We all wish we could do that. I'd love to see what's happening 50 years from now. I'd also love to go back in time. I'd love to see the day I was born and see what everyone was doing and the chaos I created.

The relationship between Doc and Marty is also so classic. A young man is exposed to this crazy character. There's no one else in the community who invents all sorts of things. He has a great music system! What kid wouldn't be fascinated by this? Doc is the super mentor for Marty.

And it's so well-directed and so well-written. It was a great collaboration. It's amazing that the story could have been done in three films. A film that follows up on the original usually doesn't live up to expectations, but these do. It has a lot of momentum and enjoyment and excitement. And it has endured. It hasn't aged in a way that makes it old. It's still alive and contemporary.

Right, there's something about the guy with crazy hair who can show you the mysteries of the universe.

I was always fascinated by scientists growing up. I read biographies of Albert Einstein. He was able to imagine the answers to how the universe works. It amazes me even now. I don't think I'm alone in that. It's an incredible gift, to take a monumental problem and find a solution, to put the workings of the universe in an equation.

Einstein seems like a natural influence for Doc Brown.

In addition to Einstein, there was a classical conductor named Leopold Stokowski who was the conductor of the Philadelphia Orchestra. He made innovations in the way he approached classical music. I grew up in a classical milieu, I grew up around a lot of classical musicians. I heard a recording on the radio of Gustav Holst, a British composer, called The Planets. Leopold Stokowski conducted it, and on the cover of the record album was a picture of him conducting and swirling around him was the solar system. He had long hair and his whole presence was that ... I wish I knew him. That record album was very inspiring.

My father saw it and said, "He's a great musician but why does he have to have his hair like that?"

Is that your most Philadelphia experience?

I was with a tour of A Midsummer Night's Dream with Bert Lahr. He played Bottom. It was a six month national tour in 1960, and we came to play Philadelphia for two or three weeks. I was an understudy. I was one of the spirit creatures that followed Oberon, part of his entourage. I was just getting my feet wet.

I've been there incidentally over my life. It has a feeling of brotherly love. There's a tone there that's wonderful.

The last time you were here, it was a reunion with Michael J. Fox and Lea Thompson for last year's Wizard World.

I love to see Michael, he's such an extraordinary person. He's dealt with the cards handed to him. He has such humor and intelligence. He has a drive where he doesn't care, he just keeps doing what he does. It's great. He was 21 or 22 during the movie, but he has a kid's persona to him. In a sense, he hasn't grown up yet. He loves to play, he has a great spirit.

Back to the Future with Christopher Lloyd, 7:30 p.m. Saturday, Keswick Theatre, 291 N. Keswick Ave., Glenside, Pa., $39.50-$150, 215-572-7650.

meichel@phillynews.com

215-854-5909 @mollyeichel