Actors that have co-starred with Robin were devastated to learn of his death...
Robin Williams, the Oscar award-winning actor behind such memorable characters as Mrs. Doubtfire and Patch Adams, died Monday at the age of 63. While his cause of death has not yet been confirmed, it is suspected that he died from asphyxiation from apparent suicide. A publicist for Williams confirmed the actor's death this morning, calling it a "tragic and sudden loss."
Williams starred in dozens of movies and television shows over his more than 40 years in show business. Many of his former co-stars took to their Twitter accounts after his death was reported to mourn the loss of one of Hollywood's funniest actors.

Robin Williams has died. (Fame FlyNet UK)
Henry Winkler, who in the late 1970s starred alongside Williams on several episodes of Happy Days, expressed his admiration for Williams' ability to improvise on-camera.
Robin Williams was like no other ..To watch him create on the spot was a privilege to behold.. Robin you are an angel now !!! REST IN PEACE
— Henry Winkler (@hwinkler4real) August 11, 2014
Mara Wilson, who as a little girl starred with Williams in the 1993 comedy Mrs. Doubtfire, told her fans that she would be taking time off from social media to mourn Williams' death.
Very sad, very upset, very glad I did not have to hear about this though Twitter. Probably going to be taking some time off it for a while.
— Mara Wilson (@MaraWritesStuff) August 11, 2014
Mandy Moore, who starred with Williams in the 2007 comedy License to Wed sent her best wishes to Williams' loved ones.
Honored to have worked w such a bright light and brilliant man. Love and prayers to his family and friends. #RIPRobinWilliams
— Mandy Moore (@TheMandyMoore) August 11, 2014
Minnie Driver, Williams' co-star in the 1997 film Good Will Hunting, expressed her disbelief.
My Heart's broken. Robin was a beautiful, kind soul. Can't bear that he's gone. So incredibly sorry for his family.
— Minnie Driver (@driverminnie) August 11, 2014
Singer/actor JoJo, who starred in the 2006 family comedy RV with Williams, also mourned the actor's death.
I love you Robin. We all did/do. No one will ever compare to you. May you rest in peace.
— JoJo (@JoJoistheway) August 11, 2014
David Alan Grier, Williams' co-star in the 1995 film Jumanji, was distraught over the loss of his friend.
Rest in Peace Robin Williams. I had the honor and joy of working with him. I miss him already...
— David Alan Grier (@davidalangrier) August 11, 2014