After spending two months ensconced quietly in an Oregon rehab program, Robin Williams is back making laughs onscreen.

The 55-year-old comedian voices two characters in the animated "Happy Feet" and performs alongside an ensemble cast including Ben Stiller and Dick Van Dyke in the holiday fantasy "Night at the Museum."

He's grateful, he said, for the support of family and friends after his relapse into alcoholism earlier in the year, for which he checked into rehab on his own.

"Glad to have done it. Club medicated. Came out, happy to be around," Williams told The Associated Press in an interview. "Good to have backup."

Williams was speaking from San Francisco, where he said he'd reached that phase of Christmas shopping "where you go from hunter-gatherer to shopper-borrower."

In "Night at the Museum," which opened Friday, Williams plays a wax figure of President Theodore Roosevelt, a role the manic but brainy comedian said was "a wonderful thing."

"He was bigger than life at a time when there were big men as president — big fat men. He was a very active, vital, very well read, well-written really outspoken man," Williams said. "He was put in power by people who thought he could never do any damage. Then bang! President McKinley was assassinated and he's one of the great reformers of the early 20th century."

Williams rode a horse and acted along with Stiller in scenes with a capuchin monkey named Crystal.

"Once we started working with the monkey, we both realized we're screwed. This is over. It combines the worst aspects of working with children and animals when you have an animal that looks like a child," Williams said. "He overacts like crazy. If he made those faces as a human we'd be like, `What's he on?'

"Plus what other human can (defecate) on you in the middle of a scene and people would be like `Ahttp://wwww, great.' Basically we finished a take, and he took a dump on my shoulder. I was like OK, thank you."

Williams said he tried to soothe the animal.

"I just talked to it nice and say `Who's your daddy? Who loves you? Who's a simian? Who likes your little tail? Who's more hairy than you? I am. I'm the alpha. You know that.'"