In a statement to PEOPLE, Gellar reflects on Williams, who died of suicide Monday at the age of 63, and the indelible mark he made on her and her family. Gellar played the straightlaced daughter Sydney to Williams' eccentric ad man Simon in the CBS comedy that was cancelled in May after only one season.
"My life is a better place because I knew Robin Williams," Gellar 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. 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. Us crazy ones love you."
Gellar also went on to say, "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."
Several people who worked with Williams on The Crazy Ones told PEOPLE about how kind and affectionate the actor was to the cast and crew alike.
"He was so benevolent," said one source close to the show. "He would appreciate everyone else's work. He was the first one to say how incredible Sarah and [costar] Jimmy Wolk were. He had affection for everyone. He made sure everyone knew he was part of a team. Who does that? When you're Robin you don't have to do that."
The Crazy Ones creator David E. Kelley says in a statement to PEOPLE of Williams: "The talent was legendary. But equally inspiring, perhaps more so, was his kindness and humanity. A gentle soul who touched us all. A very special man, and our hearts are broken."
Before the comedy began its run on CBS in the fall of 2013, Gellar spoke with enthusiasm about working with a talented – and very understanding – man like Williams.
"You get lucky to work with a legendary comic and you get lucky if you get to work with an Academy Award winner and Juilliard-trained actor," she told PEOPLE in July of 2013. "I get to work with a guy who is not only talented but so kind and he understands the dilemma that I find being caught between my home life and my professional life and he couldn't be more caring. My joke is that I didn't actually apply to be on the show. I applied for Robin to adopt me."
For more on Robin Williams's tragic death and his legacy of comic genius, pick up the latest issue of PEOPLE, on newsstands Friday
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.