Williams' appeal stretched across generations and genres, from family fare as the voice of Disney's blue Genie in "Aladdin" to his portrayal of a fatherly therapist in the 1997 drama "Good Will Hunting," for which he earned his sole Oscar.
But many remembered the master of impressions on Monday for his portrayal in "Mrs. Doubtfire", when he played the part of a British nanny whose identity he assumed as a divorced father to be with his children.
"This morning, I lost my husband and my best friend, while the world lost one of its most beloved artists and beautiful human beings. I am utterly heartbroken," Williams' wife Susan Schneider said in a statement.
The Marin County Sheriff's coroner's division said it suspected Williams committed suicide by asphyxia, but the cause of death is still under investigation and an autopsy will be conducted Tuesday.
Williams had been recently suffering from severe depression, his publicist Mara Buxbaum said in a statement, and the actor had repeatedly talked about his past struggles with alcohol.
The Sheriff's office said it received an emergency call about noon local time on Monday, saying that Williams was unconscious and not breathing at his home near Tiburon, north of San Francisco.
Actor Robin Williams as T S Garp from the film, 'The World According to Garp'. (AP)
Outside the family home in a neighborhood of low-slung houses with water views, people left flowers and talked about the man who often had a smile and a wave for children on the street.
"Everyone loved him, but nobody bothered him. He would live unrecognized and just keep to himself," said neighbor Johanna Dunning, who often saw him out biking early in the morning.
Social media was alight with appreciation for Williams, who introduced his frenetic and outlandish vaudeville-esque style to audiences as a quirky extraterrestrial in the late 1970s TV comedy "Mork & Mindy."
U.S. President Barack Obama called Williams a "one of a kind" actor who could make people laugh and cry in his array of characters.
"He arrived in our lives as an alien - but he ended up touching every element of the human spirit," Obama said in a statement.
Williams, who was most recently in the CBS television comedy "The Crazy Ones" until it was canceled after one season, had entered a Minnesota rehabilitation center this summer to help him maintain sobriety.
His representatives at the time said Williams was not using drugs or alcohol but had gone to the center to "fine-tune and focus" his sobriety after working a longer-than-usual schedule.
The death of Williams shook Hollywood, and colleagues mourned the loss of what many called a big-hearted man and one of the most inventive comedians of his time.
"Robin was a lightning storm of comic genius and our laughter was the thunder that sustained him," said filmmaker Steven Spielberg, who directed Williams as Peter Pan in the 1991 film, "Hook." "He was a pal and I can't believe he's gone."
Fellow comedian Steve Martin said in a tweet: "I could not be more stunned by the loss of Robin Williams, mensch, great talent, acting partner, genuine soul."
Williams is scheduled to appear in "Night at the Museum: Secret of the Tomb" on Dec. 19, 2014, playing the statue of Teddy Roosevelt who comes to life at night. Twentieth Century Fox, which will distribute the film, had no immediate comment.
In April, the Hollywood Reporter said that Fox's Fox 2000 division was developing a sequel to his 1993 hit "Mrs. Doubtfire" that would reunite Williams and director Chris Columbus.
Williams, who was born in Chicago in 1951 and grew up in suburban Detroit earned four Academy Award nominations, the first for his portrayal of U.S. Army deejay Adrian Cronauer during the Vietnam War in "Good Morning, Vietnam."
He also earned nominations for the 1990 coming-of-age prep school drama "Dead Poets Society" and "The Fisher King" in 1991 in which he plays a homeless man who helps save a suicidal radio host.
Williams married three times, most recently in 2011 to Schneider. He has three children.
His death also deeply affected his local artists' community, far from the hype of Hollywood.
"He embodied what it meant to be humble," said Lucy Mercer, executive artistic director at Throckmorton Theatre, a small venue near Williams' home, where the actor was known to try out new material.
"He doused us in his love and positive glow and never asked for anything in return."