The actor "passed away [Monday] morning. He had been battling severe depression of late," his rep said in a statement. "This is a tragic and sudden loss. The family respectfully asks for their privacy as they grieve during this very difficult time."
Williams was found in his home in Tiburon, California, after police responded to a 911 call, PEOPLE has confirmed. He was 63.
"At this time, the Sheriff's Office Coroner Division suspects the death may be a suicide due to asphyxia, but a comprehensive investigation must be completed before a final determination is made," Lt. Keith Boyd, the Marin County assistant chief deputy coroner, said in a statement.
The Crazy Ones star checked himself into rehab in early July after battling alcohol and drug addiction throughout his life.
"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," his wife Susan Schneider said in a statement.
"On behalf of Robin's family, we are asking for privacy during our time of profound grief. 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."
Upon Williams's passing, President Barack Obama issued the following statement: "Robin Williams was an airman, a doctor, a genie, a nanny, a president, a professor, a bangarang Peter Pan and everything in between. But he was one of a kind. He arrived in our lives an alien – but he ended up touching every element of the human spirit."
The President also cited Williams's generosity in entertaining "our troops stationed abroad [and those] marginalized on our own streets."
Williams, who shot to fame in 1978 in the TV series Mork & Mindy, enjoyed a long career as a comedic and voice actor. He was in talks to reprise his role in the sequel for the popular family film Mrs. Doubtfire.
"There really are no words to describe the loss of Robin Williams," Fox network said in a statement. "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."
CBS, which last season broadcast the Williams sitcom The Crazy Ones, said in its 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."
Others who worked with Williams recalled his kindness and humor.
"He was just such a nice man," said an industry source who worked with him in 2013. "He would always say hello and ask if I needed help with anything. He was just lovely. Everyone really loved working with him."
"Nobody made the world laugh like Robin Williams," David Steinberg, his manager of 35 years, told PEOPLE. "My brother, my friend, my soul mate, I will miss you."
See how Hollywood is mourning the loss of Williams on social media below.
For more on Robin Williams's tragic death and his legacy of comic genius, pick up the latest issue of PEOPLE, on newsstands Friday
Reporting by PATRICK GOMEZ, MARY GREEN, JD HEYMAN, ELIZABETH LEONARD, GABRIELLE OLYA and LYNETTE RICE
If you or someone you know is considering suicide, please contact the National Suicide Prevention Lifeline at 1-800-273-TALK (8255).
The Williams family is asking well-wishers to send contributions to charities close to the actor's heart in lieu of flowers. Suggested organizations include St. Jude Children's Research Hospital, Challenged Athletes, USO, the Muhammad Ali Parkinson Center, the Christopher and Dana Reeve Foundation and Glide Memorial Church in San Francisco.