Age: 40
Occupation: Actor, activist
Previous TIME 100 appearances: 0
With performances in blockbusters such as The Adjustment Bureau and the Oscar-nominated True Grit, as well as a recurring role on NBC's hit comedy 30 Rock, Matt Damon dominated both the big and small screens this past year. Yet he poured equal energy into Water.org, a nonprofit he co-founded in 2009, which aims to take safe and clean drinking water to developing countries.