Jeremy Grantham
Credit: Daniel Acker / Bloomberg / Getty Images

Estimated net worth: N/A

The Boston fund manager, with $100 billion under his watch, has written about the dangers of climate change in his quarterly newsletter to investors and once attended a protest in which environmental activist Bill McKibben and actress Daryl Hannah were arrested. "What we are trying to do is . . . buy time for the world to wake up," he said.