Maria Puente

USA TODAY

In a shocking development, Oscar-winning actor/comic Robin Williams was found dead in his California home Monday, a possible suicide, according to investigators. He was 63.

The Marin County Sheriff's Office said Williams was found unconscious and not breathing inside his home in Tiburon, Calif., around noon local time, and was pronounced dead shortly after. Tiburon is across the Golden Gate Bridge north of San Francisco.

The sheriff's press release identified him by his full name, Robin McLaurin Williams. Investigators also said they will hold a news conference Tuesday at 11 a.m. PT (2 p.m. ET).

The county coroner suspects the death was "a suicide due to asphyxia," which could mean death by hanging. But a comprehensive investigation must be completed before a final determination is made; an autopsy is scheduled for Tuesday, the press release said.

Williams' rep confirmed the death to USA TODAY.

"Robin Williams passed away this morning," said Mara Buxbaum, president of his PR firm. "He has been battling severe depression of late. This is a tragic and sudden loss. The family respectfully asks for their privacy as they grieve during this very difficult time."

His wife, Susan Schneider, issued a brief 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. I am utterly heartbroken," she said.

The news of his death sent shock waves through Hollywood and the nation, and prompted an outpouring of grieving tweets and statements from everyone from the president of the United States to the Sesame Street gang.

"Robin Williams was an airman, a doctor, a genie, a nanny, a president, a professor, a bangarang Peter Pan, and everything in between," President Obama said in a statement. "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. He made us laugh. He made us cry. 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. The Obama family offers our condolences to Robin's family, his friends, and everyone who found their voice and their verse thanks to Robin Williams."

CNN reported a statement from Pam Dawber, Williams' co-star in the wacky Mork & Mindy of the late 1970s, which introduced Williams to an amazed nation. "I am completely and totally devastated. What more can be said?!" Dawber said.

"We mourn the loss of our friend Robin Williams, who always made us laugh and smile," the Sesame Street tweet read.

"I saw him on stage the very first time he auditioned at The Improv in Los Angeles," said Jay Leno in a statement. "And we have been friends ever since. It's a very sad day."

Williams' last tweet and Instagram was on July 31, when he wished his daughter, Zelda Rae, a happy 25th birthday and posted a picture of himself with her as a child. "Quarter of a century old today but always my baby girl," he captioned the photo.

In San Francisco, where Williams for a while lived in the fog-shrouded oceanside Sea Cliff neighborhood, residents were shocked and saddened.

"He seemed like a good San Franciscan," said Griff Behncke, 35, who was waiting to take the ferry ride back to Sausalito, near Tiburon. He remembers Williams donating blood after the 9/11 terror attacks, and then entertaining the long line of people waiting to donate.

Williams will reprise his role as Theodore Roosevelt in the third Night at the Museum film. Fox issued a statement, according to Entertainment Weekly.

"There really are no words to describe the loss of Robin Williams. He was immensely talented, a cherished member of our community, and part of the Fox family. Our hearts go out to his family, friends and fans. He will be deeply missed."

Williams, who won an Oscar for his supporting role in Good Will Hunting, also recently signed on to reprise his beloved role as Mrs. Doubtfire in a sequel to be directed by Chris Columbus, according to EW.

Williams has battled health problems and struggled with substance abuse for decades. Only last month he went into rehab at Hazelden Addiction Treatment Center in Minnesota, and was expected to stay there for several weeks.

CBS also issued a statement: "Our world has lost a comic genius, a gifted actor and a beautiful man. We will remember Robin Williams as one of the unique talents of his time who was loved by many, but also as a kind, caring soul, who treated his colleagues and co-workers with great affection and respect. Our heartfelt thoughts and sympathies go out to his family, loved ones and friends."

Williams talked to USA TODAY last fall before the premiere of his CBS comedy, The Crazy Ones. He talked about the favorite characters he's portrayed:

"In terms of voices, it's the genie (from Aladdin) just because it was like 32 different voices," he said. "But in terms of acting roles, I think Awakenings, because it's Oliver Sacks and he's this extraordinary man who introduced me to the whole idea that the brain is this incredible organ and all the different aspects of it. And creativity, and looking at the brain from the inside out."

Twentieth Century Fox Television, producer of The Crazy Ones, issued a statement: "Robin Williams was a comedy giant, and although we only knew him personally for a season, he was warm, funny and a true professional. His cast and crew both loved him and loved working with him, and our hearts go out to his family and friends. He was one of a kind."

Williams' many friends and admirers, famous and not famous, could barely process the news, and took to social media to mourn.

"There are many talented, legendary, iconic people in this world but Robin WIlliams could be set aside in a category apart from everyone else," said Robyn Knapton Ridgley, a Hollywood writer/producer who worked with Williams in the past. "His scintillating genius I treasure to this day."

But his epitaph could never be confined to just 140 characters. When he spoke to USA TODAY last year, he reflected on the happy point he had reached in his life.

"I'm lucky. I'm really blessed. I have a wonderful life. Good peeps." USA TODAY: Your kids? "Wonderful. And my wife. It's just a good time in my life. Wonderful place to be."

Contributing: Bill Keveney, Cindy Clark, Nancy Blair, Laura Mandaro, Beth Weise