Williams' calling card was a kind of crazed volatility, built around a genius for stream-of-consciousness improvisation. Some of this he honed, some of it was rooted somewhere deep, reflected in eyes that twinkled with mischief.
To my mind, his unique, fascinating instability was most effectively bottled and displayed in Terry Gilliam's 1991 "The Fisher King," featuring Williams as an erratic and possibly visionary homeless man befriended by Jeff Bridges. Williams was nominated for an Oscar, and won the Golden Globe, for his role.
This was Williams at the peak of his game, part of a run that started with his work as a rambunctious theater-of-war DJ in "Good Morning, Vietnam" for Barry Levinson in 1987 (Oscar-nominated), inspirational teacher in "Dead Poets Society" for Peter Weir in 1989 (Oscar-nominated), culminating with his Oscar win as the university professor who draws out Matt Damon's troubled genius in 1997's "Good Will Hunting" for Gus Van Sant (good directors brought out the best in Williams).
During that time, he had some of his biggest mass-audience hits - in drag to play a housekeeper in "Mrs. Doubtfire" (1993), portraying a clown-nosed doctor in the biopic "Patch Adams" (1998), a gay man hosting a clueless conservative politician in "The Birdcage" (1996), and of course as the voice of Genie in "Aladdin" (1992).
Many Williams buffs think some of his best comic film work can be found in his first collaboration with Gilliam, "The Adventures of Baron von Munchausen" (1988).
Gilliam was one of the first directors to figure out what to do with the dynamic Williams, a big star in stand-up and on television, where he'd starred as a space alien in the hit series "Mork & Mindy," which ran from 1978 to 1982.
He played the lead role in the Robert Altman curiosity "Popeye" (1980), then had a vivid role in "The World According to Garp" for George Roy Hill in 1982, but back then movies seemed not to know quite what to do with him. Paul Mazursky incorporated him into "Moscow on the Hudson" a few years later, but Williams was still making movies like "Club Paradise" before Levinson gave him one of his signature roles in "Good Morning, Vietnam."
What everyone knew was that Williams was a one-of-a-kind performer. This was obvious to acting instructor John Houseman, who plucked Williams from his 1973 Juilliard freshman class for special training, along with Christopher Reeve. (Williams came to Juilliard after attending high school and some college in California, although he was born in Chicago and raised for a time in Michigan.)
Williams worked throughout his adult life as a stand-up comic, and did ample charity work in that capacity alongside Billy Crystal and Whoopi Goldberg. He adapted some of his confessional routines into a well-received one-man show on Broadway, and did a variety of theater work, appearing off-Broadway with Steve Martin in "Waiting for Godot."
Martin yesterday on Twitter wrote: "I could not be more stunned by the loss of Robin Williams, mensch, great talent, acting partner, genuine soul."