More recently, he appeared in the "Night at the Museum" movies, playing President Theodore Roosevelt in the comedies in which Ben Stiller's security guard has to contend with wax figures that come alive and wreak havoc after a museum closes. The third film in the series is in post-production, according to the Internet Movie Database.
In April, Fox 2000 said it was developing a sequel to "Mrs. Doubtfire" and Williams was in talks to join the production.
Williams also made a short-lived return to TV last fall in CBS' "The Crazy Ones," a sitcom about a father-daughter ad agency team that co-starred Sarah Michelle Gellar. It was canceled after one season.
As word of his death spread, tributes from inside and outside the entertainment industry poured in.
"Robin Williams was an airman, a doctor, a genie, a nanny, a president, a professor, a bangarang Peter Pan, and everything in between. But he was one of a kind. He arrived in our lives as an alien - but he ended up touching every element of the human spirit," President Barack Obama said in a statement.
Born in Chicago in 1951, Williams would remember himself as a shy kid who got some early laughs from his mother — by mimicking his grandmother. He opened up more in high school when he joined the drama club, and he was accepted into the Juilliard Academy, where he had several classes in which he and Christopher Reeve were the only students and John Houseman was the teacher.
Encouraged by Houseman to pursue comedy, Williams identified with the wildest and angriest of performers: Jonathan Winters, Lenny Bruce, Richard Pryor, George Carlin. Their acts were not warm and lovable. They were just being themselves.
"You look at the world and see how scary it can be sometimes and still try to deal with the fear," he said in 1989. "Comedy can deal with the fear and still not paralyze you or tell you that it's going away. You say, OK, you got certain choices here, you can laugh at them and then once you've laughed at them and you have expunged the demon, now you can deal with them. That's what I do when I do my act."
He unveiled Mork, the alien from the planet Ork, in an appearance on "Happy Days" and was granted his own series, which ran from 1978 to 1982 and co-starred Pam Dawber as a woman who takes in the interplanetary visitor.
"I am completely and totally devastated," Dawber said in a statement. "What more can be said?"
Williams could handle a script, when he felt like it, and also think on his feet. He ad-libbed in many of his films and was just as quick in person. During a media tour for "Awakenings," when director Penny Marshall mistakenly described the film as being set in a "menstrual hospital," instead of "mental hospital," Williams quickly stepped in and joked, "It's a period piece."
Winner of a Grammy in 2003 for best spoken comedy album, "Robin Williams — Live 2002," he once likened his act to the daily jogs he took across the Golden Gate Bridge. There were times he would look over the edge, one side of him pulling back in fear, the other insisting he could fly.
"You have an internal critic, an internal drive that says, 'OK, you can do more.' Maybe that's what keeps you going," Williams said. "Maybe that's a demon. ... Some people say, 'It's a muse.' No, it's not a muse! It's a demon!"
In addition to his wife, Williams is survived by his three children: daughter Zelda, 25; and sons Zachary, 31, and Cody, 22.
Italie reported from New York. AP Entertainment writers Lynn Elber Derrik J. Lang and Associated Press Writer John Rogers contributed to this report.
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