Mark Zuckerberg may be worth more than $33 billion, but for his 30th birthday this May, he didn't even throw a party.

Instead, he flew to New Jersey to watch his younger sister defend her Ph.D. in classics at Princeton, Lev Grossman reports in Time. 

This isn't the first time Zuckerberg has shunned extravagance. 

Despite his billions, he reportedly drives an Acura because "it's safe and not ostentatious," and his understated wardrobe of a plain gray t-shirt or hoodie has been well documented. 

He married his longtime girlfriend Priscilla Chan outside in his backyard, and the couple even enjoyed McDonald's on their Italian honeymoon. 

One thing Zuckerberg will spend money on, however, is philanthropy. He donated a significant amount of money to Newark, New Jersey’s public-school system and was named the most charitable philanthropist in 2013 after donating a half-billion dollars of Facebook stock to the Silicon Valley Community Foundation.

He and his wife Priscilla also personally donated $25 million to the Centers for Disease Control Foundation in October to help fight Ebola. 

His largest and most ambitious charitable initiative is, which aims to get every single human being online. 

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