Facebook began trading publicly on May 18. When the market closed that day, the company's stock was valued at $38.23, up just $0.23 cents from its offering price. Zuck's net worth jumped slightly from $19.1 billion to $19.4 billion during the day.
As of Wednesday morning, Colombia's Luis Carlos Sarmiento held the number-40 spot on Bloomberg's list, with an estimated net worth of $15.5 billion.
Zuck, who married college sweetheart Priscilla Chan the day after Facebook's Nasdaq debut, doesn't seem to be wringing his hands over his billions. The couple was recently spotted honeymooning in Rome, Italy, where they enjoyed local landmarks like the Sistine Chapel and even made a quick stop at McDonald's.
The couple is known for keeping a low profile and opting for casual attire in public. Zuck, for one, dons a hooded sweatshirt more often than a three-piece suit, and Priscilla has been seen wearing a small ruby ring instead of a large diamond on her ring finger.
Writing on Quora, a man who identifies himself as former Facebook employee Ezra Callahan (2004 - 2010) explains Zuckerberg's attitude toward wealth:
"I can tell you that when I worked with Mark Zuckerberg, money was certainly not his primary motivator. He lived an absurdly spartan lifestyle. Well after the point that Facebook's valuation passed $1B, Mark still lived in a small, crappy apartment and slept on a mattress on the floor. All he really cared about was work and he spent most of his waking hours at the office, so it didn't seem to matter much to him to furnish his apartment or spend money on much of anything (food, clothes...anything really)."
As Facebook's stock continues to fluctuate, Zuck probably won't be losing a lot of sleep over his fortune.