Why Mark Zuckerberg wore a tie for an entire year

Mark Zuckerberg

Despite Mark Zuckerberg's massive fame, many Facebook users may not know everything there is to know about the social media mogul.

The CEO of the world's largest social network turned 31 on Thursday.

As a college student, Mark Zuckerberg created TheFacebook.com in hopes of gaining a few hundred users -11 years later, his site has more than 1.4 billion active users each month. Here are 11 little-known facts about the social media mogul.

1. While he was in high school, Zuckerberg co-developed a music app called Synapse Media Player. Microsoft and AOL reportedly offered him $1 million to further develop the app and wanted to hire him. Zuckerberg passed on the offer and decided to attend Harvard University, only to drop out after his sophomore year.

2. Zuckerberg is a vegetarian. He once stated that he will only eat meat if he has killed the animal himself. Interestingly enough, he "likes" McDonald's and In-Out-Burger on Facebook.

3. He met his future wife, Priscilla Chan, in line at a party for his fraternity. "He was this nerdy guy who was just a little bit out there," Chan told the New Yorker . "I remember he had these beer glasses that said 'pound include beer dot H.' It's a tag for C++. It's like college humor but with a nerdy, computer-science appeal."

4. With a net worth of $34.8 billion, he ranked #16 on Forbes' "Richest People on the Planet 2015" list.

5. His company has created or bought at least 20 different iOS applications. The priciest of the bunch was WhatsApp, which Facebook purchased for a whopping $19 billion in February 2014.

6. He works just 50-60 hours a week. During a recent Q&A , Zuckerberg said he does a great deal of thinking outside of the office about "how to connect the world and serve our community better."

7. Zuckerberg and his wife recently donated $75 million to the San Francisco General Hospital Foundation. It said the gift, which is the largest private donation received by the hospital since opening in 1994, will allow SF General to add two trauma rooms and three operating rooms and to double the size its emergency room.

8. Facebook is blue because Zuckerberg is color blind. In an interview, he said "blue is the richest color for me-I can see all of blue."

9. A black Acura TSX is his car of choice because it is "safe, comfortable and not ostentatious."

10. He owns a Hungarian sheepdog named Beast, who has a Facebook page with 2 million fans.

11. Though he is best known for wearing a gray T-shirt and hoodie, Zuck once wore a tie every day for an entire year. He outlined this reasoning on his Facebook page: "My 2009 challenge was to wear a tie for a whole year. After the start of the recession in 2008, I wanted to signal to everyone at Facebook that this was a serious year for us. Great companies thrive by investing more heavily while everyone else is cutting back during a recession. But great companies also make sure they're financially strong and sustainable. My tie was the symbol of how serious and important a year this was, and I wore it every day to show this."

Read More Judge to Facebook, Zuck: Hand over those emails!

JefferiesAnd the Best Place to Work in the global financial markets 2016 is...

Register for Financial Markets News Alerts