POOR ROBIN WILLIAMS

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 Museumfilm. 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.