On Tuesday, Ohanian took to Instagram to share a pair of then-and-now snapshots, alongside a heartfelt message.
"4 years ago you made me the happiest man in the world and our little family keeps me feeling more grateful every day," the Reddit co-founder wrote, alongside one photo of the couple at their lavish wedding, and a second photo of the pair with their 4-year-old daughter, Alexis Olympia, at the premiere of King Richard on Sunday.
"Nov 16 will always be a very special day for our family ♥️ happy anniversary @serenawilliams," he continued. "Thank you for bringing this joy named Olympia into our life even though you always fall asleep in the middle of our movie nights."
Shortly after Ohanian's post, Williams shared a slideshow of family photos as well.
Some of the pics are adorable candid photos of the happy couple, as well as some snapshots of them with their daughter when she was a baby. The final photo was also of them all together at Sunday's red carpet premiere.
"4 years later on this special day. I have so many fun memories. Stroll down memory lane with me," she wrote. "@alexisohanian here’s to making each day together special. Happy anniversary 🥂"
The film -- starring Will Smith as the Williams' sisters' father, Richard Williams -- tells the story of their childhood, and their father's remarkable and ambitious efforts to help his daughters achieve their tennis dreams.
While the film tells her father's story, the tennis legend stressed the importance of the audience not only seeing her father portrayed in the "right way" on screen, but her mother as well, who she called "the backbone" of their family.
"Most people just know about my dad, who was amazing and is amazing, and no one really knows the work that my mom did, and just kind of being the backbone of the family," the tennis star continued. "It just tells a little bit of all of that."
Ohanian also spoke with ET and revealed what an emotional experience it was for his wife to watch a movie about her own life and upbringing.
"Experiencing it second hand, remarkable. The first time she saw the screening of it -- cried the entire time. I think there's that surreal moment where you see your story played out, the way Will and everyone did such an amazing job with it," Ohanian gushed.