''Now don't sit on the keyboard!'' Williams said, coaxing laughs from a few dozen people in a Manhattan studio.
How did he get there Explaining it would take twice as long as it took to actually happen. Would anyone else in the world have made such a leap
Not a chance. Williams, who died in an apparent suicide Monday, was a comic force of nature. The world got to know him as the wild alien in ''Mork & Mindy,'' a comedian who elevated improvisation to an art form and also demonstrated a rare versatility in more serious roles. He moved seamlessly from comedy to drama to tragedy to comedy again during a Hollywood heyday in the 1980s and 1990s. His Academy Award as a supporting actor in ''Good Will Hunting'' came in a drama.
In 1997, Entertainment Weekly magazine named Williams the funniest man alive, and the very next year listed him as one of the world's 25 best actors - a double distinction that made him rare, if not unique.
He touched every generation and demographic, making his entrance in a 1970s comic generation with Steve Martin, John Belushi, Dan Aykroyd and Billy Crystal. He exploded onto the scene at a time when two schools of comedy dominated - ''Saturday Night Live'' and Johnny Carson - and Williams felt equally comfortable running with both crowds.
Williams was the voice of a genie in ''Aladdin'' and a hyper disc jockey in ''Good Morning Vietnam.'' In ''Mrs. Doubtfire,'' he played a dad who dressed as a woman to see his kids, and in ''Birdcage,'' he played a gay man. He was an English teacher in ''Dead Poets Society,'' a scientist in ''Awakenings'' and a prisoner of war in ''Jakob the Liar.'' In this year's independent film, ''The Angriest Man in Brooklyn,'' Williams played a man mistakenly told he had 90 minutes to live.
On a stage, in front of the lights, is where Williams shined most brightly. The riffs, tangents and impersonations came rushing at the audience, a seemingly endless torrent. It looked like onstage cocaine, a drug he abused in real life and, of course, made part of his comedy.
''Cocaine is God's way of telling you you are making too much money,'' he would say.
On a television talk show, hosts knew Williams barely needed to be wound up. Sometimes, he needed only an audience of one: Williams visited Christopher Reeve a week after the actor's horseback riding accident, dressed in scrubs with a surgical mask and speaking in a Russian accent.
The roles became less prominent as he aged and a different generation took the spotlight. Last year. CBS cast him as the star of a sitcom, ''The Crazy Ones,'' in which Williams played the colorful elder statesman at a Chicago ad agency. The network had high hopes for the comedy, which also starred Sarah Michelle Gellar, but they quickly faded and the show was cancelled after one season.
That didn't make Williams unique - Michael J. Fox also failed in a recent return to television - but it was an indication that Williams was no longer a sure ticket to success.
Like many comedians, Williams often seemed driven by demons. He had a complicated personal life, suffered from depression and was treated for substance abuse, most recently earlier this summer. He did a few lines of cocaine with John Belushi on the last night of that comic's life.
A darkness seeped in during an interview with comedian Marc Maron in 2010, where Williams seemingly dismissed what would be a career highlight for many actors. ''People say you're an Academy Award winner,'' he said. ''The Academy Award lasted about a week and then one week later, people went, `Hey Mork!'''
Stand-up comedy was where Williams got the most satisfaction.
''You get the feedback,'' Williams said in a 2007 interview with The Associated Press. ''There's an energy. It's live theater. That's why I think actors like that. You know, musicians need it, comedians definitely need it. It doesn't matter what size and what club, whether it's 30 people in the club or 2,000 in a hall or a theater. It's live, it's symbiotic, you need it.''
In the 2013 Sirius appearance with Whoopi Goldberg, his comic colleague had no trouble encouraging a visit from Elmer Fudd, one of the many voices Williams could instantly slip into.
Instantly, ''Elmer'' was singing Bruce Springsteen: ''I'm dwivin' in my car...''
Ultimately, Williams had needs no one could meet. The millions of people he made laugh over nearly four decades in the public consciousness weren't enough.