(CNN) -- Robin Williams delighted fans with his off-the-wall, high-energy comedy that took unexpected turn after unexpected turn.
He was a comedic inspiration for many performers, but he also was a brilliant dramatic actor on stage and on the big screen.
Those who worked with him knew him to be a genius and the rarest of talents. After news of his shocking death spread, his friends and professional admirers expressed their love for the man Steve Martin called a "great talent, acting partner, genuine soul."
For Sarah Michelle Gellar, who co-starred with Williams in the CBS comedy "The Crazy Ones," he was the father figure she'd always "dreamed of having."
"My life is a better place because I knew Robin Williams," the 37-year-old actress said in a statement to People magazine. "The Crazy Ones" only lasted for a season, but it was more than enough time for the pair who played a father and daughter onscreen to form a similar bond off the set.
To Gellar's two children with actor Freddie Prinze Jr., Williams was "Uncle Robin," the actress said. "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." (It's been reported that Gellar was estranged from her biological father.)
On Twitter on Monday, Gellar joined the wave of those sharing their grief and memories, posting a series of photos of herself with her former co-star.
"There are not enough adjectives to describe the light he was, to anyone that ever had the pleasure to meet him," she told People. "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."
When Conan O'Brien heard the news, he was near the end of taping Monday's edition of "Conan" with Will Arnett.
"This is unusual and upsetting, but we got some news during the show that Robin Williams has passed away," O'Brien said, apologizing to those in the studio audience who were hearing the news for the first time. "This is absolutely shocking, and horrifying, and so upsetting on every level. ... and it felt like we just needed to acknowledge. We're absolutely stunned."
Chimed in Arnett, "As funny as he was, he's truly one of the all-time greats, he was even better as a person. He was even more fantastic. One of the loveliest, sweetest, kindest guys I've ever worked with. ... It's a major, major loss for everybody."
As he closed the show, O'Brien said, "We're thinking of Robin's family. We're thinking about everybody who he touched around the world, throughout his life. We're thinking about Robin tonight."
As were several. Below is just a sampling of the thoughts shared in light of Williams' death.
Absolutely stunned to hear the news about Robin Williams. It's unimaginable to me that we've lost such a genuinely funny and sweet man.— Conan O'Brien (@ConanOBrien) August 12, 2014
I can't believe the news about Robin Williams. He gave so much to so many people. I'm heartbroken.— Ellen DeGeneres (@TheEllenShow) August 11, 2014
I could not be more stunned by the loss of Robin Williams, mensch, great talent, acting partner, genuine soul.— Steve Martin (@SteveMartinToGo) August 11, 2014
His heart was as big as his genius. So sad. Rest in Peace Robin Williams.— bob saget (@bobsaget) August 11, 2014
Oh Robin...Our hearts are broken. Rest in peace darling. We loved you.— Goldie Hawn (@goldiehawn) August 11, 2014
When I was 18 I got a job as an intern at Comic Relief just to be near him. A genius and a truly kind man who made the world a better place.— Judd Apatow (@JuddApatow) August 12, 2014
Robin Williams has died and I am very sad. From every comedian here at the Edinburgh Fringe Festival, we salute him & we say goodbye— Eddie Izzard (@eddieizzard) August 11, 2014
Ah Robin, I'm so sorry the earth couldn't stay worthy of you. Hope happiness awaits you.— jason alexander (@IJasonAlexander) August 11, 2014
Robin Williams RIP. Truly one of the most talented men in the history of show business. What a loss. To lose those who make us laugh...wow.— Wayne Brady (@waynebrady) August 12, 2014
Robin Williams ~ Vaya Con Dios my friend , I love you— George Lopez (@georgelopez) August 11, 2014
RIP mr Williams - beyond great talent -such a kind and lovely person— John Cusack (@johncusack) August 11, 2014
One of the greatest nights of my youth was spent with dear Robin Williams. Let's all get closer to our friends who are down, and share love.— Val Kilmer (@ValEKilmer) August 12, 2014
So sad Robin Williams died :( We did 2 films 2gether. He ws a very lovely man & kind caring person. My heart goes out 2 his loved ones.— Fran Drescher (@frandrescher) August 11, 2014
I'm in utter disbelief that Robin Williams is dead.— Dane Cook (@DaneCook) August 11, 2014
CNN's Chandler Friedman, Henry Hanks, Topher Gauk-Roger and Breeanna Hare contributed to this report.