NEW YORK (AP) -- Fans of Sam Rockwell have often had to resort to limited glimpses of him in supporting, character-actor roles. In his new film, "Moon," that's far from a concern.

Rockwell is very nearly the only actor in "Moon." And there's more than one of him.

He plays astronaut Sam Bell, who's living alone on the far side of the moon, finishing his three-year contract harvesting lunar rock for energy on Earth. When Bell's health begins deteriorating, he starts seeing a younger version of himself around the base.

That the movie is a showcase for the 40-year-old is somewhat intentional: For his first film, Duncan Jones wrote the part specifically for the actor, designing an "acting challenge" meant to be too intriguing for Rockwell to turn down.

"I just thought it was sacrilegious that there weren't more roles where he was the leading man," said Jones, the son of David Bowie.

Rockwell has shown a talent for portraying characters on the margins. His outsiders sometimes reside happily on the fringe — as in his early breakthrough performance as an "off-the-grid" loner in Tom DiCillo's "Box of Moonlight" (1996) — or desperately want back in, as in his talk-show host-hitman in George Clooney's "Confessions of a Dangerous Mind" (2002).

In an interview last month, Rockwell said his impulse for such roles comes from the `70s cinema of alienation — movies like "Taxi Driver" and "Midnight Cowboy."

"Those films are just constantly coming back to me," said Rockwell. "That's just the reason I act, is to sort of recreate those films in my mind, to do my own version of that."

After "Box of Moonlight," he had memorable roles in "The Green Mile," "Galaxy Quest," "Charlie's Angels" and "Matchstick Men," opposite Nicolas Cage.

Film critic Roger Ebert has called him "your go-to guy for weirdness," comparing him to Christopher Walken. Rockwell, whose recent notable credits include "Frost/Nixon" and "The Assassination of Jesse James by the Coward Robert Ford," was always interested in darker material, but began to notice he was mostly offered comedies that sought to mine his oddball tendencies a bit too obviously.

The little-seen and underrated "Snow Angels" of 2007 was a line in the sand for Rockwell — "not that anyone else noticed," he notes — playing an estranged (and deranged) husband bent on winning back his wife.

"I was getting some comedies and stuff — and I love comedy — but I just wanted to kind of make a statement, sort of an artistic statement," said Rockwell. "You really kind of have to stick to your guns because people want you to do certain things."

Trying to get into the heads of the various Sam Bells, Rockwell says, was "like a Rubik's Cube for actors. ... a fascinating Freudian game to play on yourself."

He was often acting only with a tennis ball or a piece of tape, small signifiers marking where the other Sam Bell would be. The maneuvering meant there was only so much room for improvising, but Rockwell would find "small windows" where he could insert a line, so long as his timing was right.

In the course of an interview, Rockwell's love of movies was easily evident. As touchstones for the characters, he delved into David Cronenberg's "Dead Ringers." He expressed admiration for Michael Keaton in "Multiplicity." And he said he "literally stole" from Dustin Hoffman's Ratso Rizzo in "Midnight Cowboy."

Rockwell considers "Moon" one of a handful of films — along with "Box of Moonlight," "Confessions" and "Snow Angels" — where he made "a growth spurt creatively."

He's also about to make a growth spurt commercially, co-starring in the "Iron Man" sequel, in which he plays Justin Hammer, the industrialist rival of Tony Stark.

Rockwell said he received the script only a week before shooting, so he "kind of took it on faith."

"It's not dissimilar to other studio movies, but the thing that's different about it is (director Jon Favreau) really likes to improvise," said Rockwell. "So we get to play more on this movie than you would on a lot of studio movies."