In this way, Grantham's approach to the environment is very much like his approach to investing. He searches for just the right opportunity - whether it's battling infestation in American forests or planting trees in Panama - and runs with it. "He places bets on people and ideas the same way he invests money," Roberts says. "He looks for inspiring people who have great ideas, helps refine those ideas, and then gives them the resources to take those ideas to scale. And he's been very successful at it."

Not that Grantham would trumpet the fact. He's not a limelight seeker; he's content to work behind the scenes at his cluttered desk, ferreting out the long-term trends that are going to change the markets and the world. "I just try to be right more often than not," Grantham says, smiling at the understatement. "And it's worked, I must say."

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Master Class

Jeremy Grantham may seem like an unassuming type with his avuncular sweep of white hair and rumpled clothes. But when it comes to saying what he thinks, he's brutally honest - and has no fear about upending conventional wisdom. A Grantham classic: "Very hard work gets in the way of thinking." He's also famous for saying that just one or two good investing ideas a year are sufficient. (He's since amended that - to one idea every couple of years.) So we administered the truth serum and asked Grantham for his unvarnished opinion of the hot-button issues roiling the world economy.

On Oil: "It's a finite resource meeting the world's most inept energy policy. It's not renewable; we're eventually going to pump it all, and yet American drivers can't stand a higher tax on gas. Europeans live with gas at $7 or $8 a gallon, but Americans can't. It's a sacred cow."