Robin Williams' Son Remembers Actor on What Would've Been His 73rd Birthday

Robin Williams is gone but not forgotten, especially to those closest to him.

On Sunday, the late actor's son, Zak Williams, paid tribute to his dad by celebrating what would have been Robin's 73rd birthday. The Mrs. Doubtfire star -- who is widely regarded as one of the greatest comedians of all time -- took his own life in August 2014 at the age of 63.

"Dad, on what would be your 73rd birthday, I remember you for all the hope and joy you brought to the world. There's not a week that goes by without someone sharing with me how you helped them through a dark time or a rough patch," Zak, 41, penned in his X (formerly Twitter) tribute.

He continued, "I'm so grateful to be your son. Love you forever."

Zak -- born Zachary Pym Williams -- is one of the Jumanji actor's three children from two of his marriages. Zak hails from Robin's marriage toValerie Velardi -- whom Robin was married to from 1978 to 1988 -- while Zelda and Cody Williams were both born during his 21-year marriage withMarsha Garces Williams.

Just last year, Zelda -- who has gone on to pave an illustrious career in Hollywood for herself, directing February's Lisa Frankenstein starring Cole Sprouse and Kathryn Newton -- similarly memorialized her dad on his birthday, which fell at the beginning of the SAG-AFTRA strike .

"Happy birthday to Poppo, who definitely would've been out there fighting the good fight for art and artists today and always," she wrote at the time, attaching a picture of her dad on a picket line from the historic 2008 Writers Guild of America strike.

Earlier this year, ET spoke with the 34-year-old director from the premiere of Lisa Frankenstein, where she shared her earliest memories of visiting her dad on set.

"I was fascinated by it early," Zelda said of Robin's work in the arts. "When you're that young, I don't think you grasp that it's a job, really; just like a fun thing you go and visit." She recalled visiting her father on the set of the1999 sci-fi comedy-drama Bicentennial Man , directed by Chris Columbus.

"That was when I was old enough to really understand that there was a whole bunch of jobs you could also do," Zelda shared. "And that set was really beautiful. Chris Columbus runs a really wonderful set and he's such a kind human that I think you weren't walking into a space that felt tense as well."

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