Since then, he's become a household name with a net worth of $79.7 billion, according to Forbes.
Here are five fast facts to know about the 36-year-old:
1. Harvard gave him an honorary degree
Zuckerberg received an honorary degree from Harvard in 2017, 12 years after he dropped out to focus on Facebook. He spoke at the college's commencement that year and was introduced as "Dr. Mark Zuckerberg."
"If I get through this speech today it'll be the first time I actually finish something here at Harvard," Zuckerberg told graduates.
2. He's a girl dad.
Zuckerberg and his wife Priscilla Chan, a pediatrician, have two daughters, August and Maxima. Zuckerberg took two months of paternity leave after both girls were born and offers Facebook employees up to four months of parental leave, People reported.
"Studies show that when working parents take time to be with their newborns, outcomes are better for the children and families," he wrote on Facebook in 2015.
3. "The Social Network" tells his story
Facebook's early days and Zuckerberg's clashes with his co-founders play out in the 2010 film "The Social Network." Jesse Eisenberg portrays Zuckerberg, and prominent actors including Andrew Garfield, Armie Hammer and Rooney Mara round out the cast.
4. He and his wife have had fertility struggles.
Zuckerberg and Chan have been open about their fertility struggles, including Chan's miscarriages before she gave birth to their eldest daughter. Zuckerberg has said he hopes sharing about their experience will give other couples hope.
"You feel so hopeful when you learn you're going to have a child," Zuckerberg wrote on Facebook in 2015. "You start imagining who they'll become and dreaming of hopes for their future. You start making plans, and then they're gone. It's a lonely experience."
5. Being an entrepreneur runs in the Zuckerberg family.
Like Zuckerberg, his older sister Randi Zuckerberg is also an entrepreneur. She founded marketing firm Zuckerberg Media. She graduated from Harvard in 2003.
Randi Zuckerberg worked at Facebook during its earlier days and is credited with helping to create Facebook Live, one of the platform's pivotal features that was introduced in 2016.
The Associated Press contributed to this report.