The actress, who played the actor's daughter on CBS' The Crazy Ones, mourned her late co-star in a statement Tuesday. "My life is a better place because I knew Robin Williams," Gellar, 37, said. "To my children he was Uncle Robin, to everyone he worked with, he was the best boss anyone had ever known, and to me he was not just an inspiration but he was the father I had always dreamed of having."
(Gellar was long estranged with her biological father, who died in 2001.)
"There are not enough adjectives to describe the light he was, to anyone that ever had the pleasure to meet him. I will miss him everyday, but I know the memory of him will live on. And to his family, I thank them for letting us know him and seeing the joy they brought him," she added. "Us crazy ones love you."
The grieving actress also wished to share the Serenity Prayer: "God, grant me the serenity to accept the things I cannot change, the courage to change the things I can, and the wisdom to know the difference."
While promoting The Crazy Ones last fall, Gellar called him "a legend." She also told E! News that he was the "greatest stand-up comedian of all time, [an] Academy Award winner and nicest man on the planet."
The half-hour sitcom was canceled after one season, but series creator David E. Kelley will remember Williams fondly. "The talent was legendary. But equally inspiring, perhaps more so, was his kindness and humanity," he told E! News. "A gentle soul who touched us all. A very special man, and our hearts are broken."
Meanwhile, actress Jessica Chastain wrote a heartfelt tribute to Williams and posted it on Facebook. "Robin Williams changed my life. He was a great actor and a generous person. Through a scholarship, he made it possible for me to graduate college," the Oscar-nominated Juilliard School alumna wrote. "His generous spirit will forever inspire me to support others as he supported me. He will forever be missed."
When she was profiled in Interview several years ago, Chastain elaborated on Williams' generosity. "I'm the first person in my family to go to college. We didn't have a lot of money, and Juilliard is a pretty expensive school," she said. "Robin Williams is a very generous Juilliard alumnus, and gives a scholarship every two years to a student, and it pays for everything, and I got it. I still haven't gotten to meet him."
When she appeared on NBC's Late Night With Jimmy Fallon in January 2013, the Zero Dark Thirty star made an on-air plea to meet Williams. "I sent him a letter when I got the scholarship, but I've never met him," she recalled. "I almost met him; I was at a restaurant and I was telling someone the story...[and] Robin came in and sat down next to me. I waited until he was done eating because I don't want to be the crazy girl at the restaurant, and before he finished he jumped up and left and I jumped up and I was gonna chase after him and then I thought, 'No!'" It's unclear if Chastain, 37, ever met her benefactor, 63.
Williams is survived by his wife, Susan Schneider, and his three children from previous marriages.
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If you or someone you know needs help, please call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255).