Robin Williams, the comedian who evolved into the surprisingly nuanced, Academy Award-winning actor, imbuing his performances with wild inventiveness and a kind of manic energy, died on Monday at his home in Tiburon, Calif., north of San Francisco. He was 63.

The Marin County sheriff’s office said in a statement that it “suspects the death to be a suicide due to asphyxia.” An investigation was underway.

The statement said that the office received a 911 call at 11:55 a.m. Pacific time, saying that a man had been found “unconscious and not breathing inside his residence.” Emergency personnel sent to the scene identified him as Mr. Williams and pronounced him dead at 12:02 p.m.

Mr. Williams’s publicist, Mara Buxbaum, said in a statement that Mr. Williams “has been battling severe depression.”

His wife, Susan Schneider, said in a statement, “This morning, I lost my husband and my best friend, while the world lost one of its most beloved artists and beautiful human beings.” She added: “As he is remembered, it is our hope the focus will not be on Robin’s death, but on the countless moments of joy and laughter he gave to millions.”

The privileged son of a Detroit auto executive who grew up chubby and lonesome, playing by himself with 2,000 toy soldiers in an empty room of a suburban mansion, Mr. Williams, as a boy, hardly fit the stereotype of someone who would grow to become a brainy comedian, or a goofy one, but he was both. Onstage he was known for ricochet riffs on politics, social issues and cultural matters both high and low; tales of drug and alcohol abuse; lewd commentaries on relations between the sexes; and lightning-like improvisations on anything an audience member might toss at him. His gigs were always rife with frenetic, spot-on impersonations that included Hollywood stars, presidents, princes, prime ministers, popes and anonymous citizens of the world. His irreverence was legendary and uncurtailable.

“Chuck, Cam, great to see you,” he once called out from a London stage at Charles, Prince of Wales, and his wife, Lady Camilla Bowles. “Yo yo, wussup Wales, House of Windsor, keepin’ it real!”

And yet he never seemed to offend.

Almost from the moment that he first uttered the greeting “Nanoo, nanoo” as Mork from Ork, an alien who befriends a wholesome young Colorado woman (Pam Dawber), on the sitcom “Mork and Mindy,” Mr. Williams was a comedy celebrity. “Mork and Mindy” made its debut on ABC in September 1978, and within two weeks had reached No. 7 in the Nielsen ratings. By the spring of 1979, 60 million viewers were tuning in to “Mork and Mindy” each week to watch Mr. Williams drink water through his finger, stand on his head when told to sit down, speak gibberish words like “shazbot” and “nimnul” that came to have meaning when he used them, and misinterpret, in startlingly literal fashion, the ordinary idioms of modern life.

He went on to earn Academy Award nominations for his roles in films like “Good Morning, Vietnam,” in which he played a loquacious radio D.J.; “Dead Poets Society,” playing a mentor to students in need of inspiration; and “The Fisher King,” as a homeless man whose life has been struck by tragedy. He won an Oscar in 1998 for “Good Will Hunting,” playing a therapist who works with a troubled prodigy played by Matt Damon.

In a statement, President Obama said of Mr. Williams, “He gave his immeasurable talent freely and generously to those who needed it most — from our troops stationed abroad to the marginalized on our own streets.”

Robin McLaurin Williams was born in Chicago on July 21, 1951, and was raised in Bloomfield Hills, Mich., and Marin County. He studied acting at the Juilliard School.

He is survived by a son, Zak, from his marriage to Valerie Velardi, and a daughter, Zelda, and a son, Cody, from his marriage to Marsha Garces.

Beginning with roles in the 1977 sex farce “Can I Do It ‘Til I Need Glasses?” and “The Richard Pryor Show,” a variety series hosted by one of his comedy mentors, Mr. Williams rapidly ascended the entertainment industry’s ladder.

Soon after “Mork and Mindy” made him a star, Mr. Williams graduated into movie roles that included the title characters in “Popeye,” Robert Altman’s 1980 live-action musical about that spinach-gulping cartoon sailor, and “The World According to Garp,” the director George Roy Hill’s 1982 adaptation of the John Irving novel.

He also continued to appear in raucous stand-up comedy specials like “Robin Williams: An Evening at the Met,” which showcased his garrulous performance style and his indefatigable ability to free-associate without the apparent benefit of prepared material. Alongside his friends and fellow actors Billy Crystal and Whoopi Goldberg, Mr. Williams appeared in an annual series of HBO telethons for Comic Relief, a charity organization that helps homeless people and others in need.

Mr. Williams’s acting career reached a new height in 1987 with his performance in Barry Levinson’s film “Good Morning, Vietnam,” in which he played Adrian Cronauer, a nonconformist Armed Forces Radio host working in Saigon in the 1960s. It earned Mr. Williams his first Oscar nomination. He earned another, two years later, for “Dead Poets Society,” directed by Peter Weir and released in 1989, in which he played an unconventional English teacher at a 1950s boarding school who inspires his students to tear up their textbooks and seize the day. (Or, as Mr. Williams’s character famously put it in the original Latin, “Carpe diem.”)

In dozens of film roles that followed, Mr. Williams could be warm and zany, whether providing the voice of an irrepressible magic genie in “Aladdin,” the 1992 animated Walt Disney feature, or playing a man who cross-dresses as a British housekeeper in “Mrs. Doubtfire,” a 1993 family comedy, or a doctor struggling to treat patients with an unknown neurological malady in “Awakenings,” the 1990 Penny Marshall drama adapted from the Oliver Sacks memoir.

Some of Mr. Williams’s performances were criticized for a mawkish sentimentality, like “Patch Adams,” a 1998 film that once again cast him as a good-hearted doctor, and “Bicentennial Man,” a 1999 science-fiction feature in which he played an android.

But Mr. Williams continued to keep audiences guessing. In addition to his Oscar-winning role in “Good Will Hunting,” which saw him play a gently humorous therapist, his résumé included roles as a villainous crime writer in “Insomnia,” Christopher Nolan’s 2002 thriller; Teddy Roosevelt in the “Night at the Museum” movies; and Dwight D. Eisenhower in the 2013 drama “Lee Daniels’ The Butler.”

Mr. Williams made his acting debut on Broadway in 2011 in “Bengal Tiger at the Baghdad Zoo,” a play written by Rajiv Joseph and set amid the American invasion of Iraq. In 2013, Mr. Williams returned to series television in “The Crazy Ones,” a CBS comedy that cast him as an idiosyncratic advertising executive, but it was canceled after one season.

Mr. Williams had completed work on several films that have not yet been released, including a third installment of the “Night at the Museum” franchise that Fox has scheduled for December, and “Merry Friggin’ Christmas,” an independent comedy about a dysfunctional family. He also provided the voice of an animated character called Dennis the Dog in a British comedy, “Absolutely Anything,” that is planned for release next year, and appeared in “Boulevard,” an independent movie that was shown at the Tribeca Film Festival but does not yet have theatrical distribution.

Mr. Williams was an admitted abuser of cocaine — which he also referred to as “Peruvian marching powder” and “the devil’s dandruff” — in the 1970s and ‘80s, and addressed his drug habit in his comedy act. “What a wonderful drug,” he said in a sardonic routine from “Live at the Met.” “Anything that makes you paranoid and impotent, give me more of that.”

In 2006, he checked himself into the Hazelden center in Springbrook, Ore., to be treated for an addiction to alcohol, having fallen off the wagon after some 20 years of sobriety.

He later explained in an interview with ABC’s Diane Sawyer that this addiction had not been “caused by anything, it’s just there.”

“It waits,” Mr. Williams continued. “It lays in wait for the time when you think, ‘It’s fine now, I’m O.K.’ Then, the next thing you know, it’s not O.K. Then you realize, ‘Where am I? I didn’t realize I was in Cleveland.’ ”

In 2009, he underwent heart surgery for an aortic valve replacement at the Cleveland Clinic in Ohio, an event that Mr. Williams said caused him to take stock of his life.

“You appreciate little things,” he said in an interview in The New York Times, “like walks on the beach with a defibrillator.”

More seriously, Mr. Williams said he had reassessed himself as a performer. “How much more can you give?” he told The Times. “Other than, literally, open-heart surgery onstage? Not much. But the only cure you have right now is the honesty of going, this is who you are. I know who I am.”

Earlier this year, Mr. Williams checked himself into a rehab facility. His publicist told People magazine that he was “taking the opportunity to fine-tune and focus on his continued commitment, of which he remains extremely proud.”