Jeff Skoll
Credit: Sarjoun Faour Photography / Getty Images

Estimated net worth: $3.8 billion

EBay's first employee, later its president, Skoll has used his billions to become a jack-of-all-philanthropies, with a special focus on climate change. He bankrolled and produced the Oscar-winning documentary An Inconvenient Truth and launched the Skoll Global Threats Fund to confront problems "imperiling humanity."