#4 Michael BloombergAmount donated in 2013: $452 million
Net worth: $31 billion
Beneficiary: Arts, education, environment, public health and other causes
Background: Michael Rubens Bloomberg is an American businessman, politician and philanthropist. He served as the 108th Mayor of New York City, holding office for three consecutive terms beginning with his first election in 2001. With a net worth of $31 billion, he is the tenth-richest person in the United States and the thirteenth-wealthiest in the world.