The head of Columbia University's Earth Institute, founder of the non-profit group Millennium Promise, and friend of Angelina and Bono, Sachs may very well be the only economist you've ever heard of.

Considering Sachs turned out to be a Harvard economist, it's probably not so surprising to hear he was a math genius as a kid. The son of famous labor lawyer Ted Sachs, Jeff was taking college-level classes in mathematics by the time he'd reached middle school. He later attended Harvard, stuck around to earn a Ph.D. by the time he was 25, and earned tenure three years later. For a decade, Sachs was a Harvard professor, earning recognition as an authority on international macro-economics. In the mid-1980s he transferred his classroom expertise to the real world when he helped the floundering Bolivian government solve their extraordinary inflation problem. Earning the moniker "Dr. Shock" for his radical approaches to solving serious economic problems, he took his formula on the road, which ended up working in some countries (Bolivia, Poland) but proved substantially less successful in others (such as Russia, where his shock therapy was an out and out disaster). In the late 1990s Sachs retreated to the classrooms of Cambridge, before moving to Columbia in 2002 when he was appointed director of the Earth Institute. He now tackles thorny problems like poverty, HIV/AIDS, and climate change, runs the non-profit Millennium Promise, publishes books, and cavorts with celebs.

Sachs's goals aren't particularly modest: He's said that by implementing a series of measures—poverty reduction, debt cancellation, and disease control—"we can realistically envision a world without extreme poverty by 2025." It's a bold statement but it's earned him legions of famous fans. Over the last few years, he's become a friend to do-gooder celebrities like Bono and Angelina Jolie, raised millions in funding from the richest people in the world and earned a spot on the bestsellers list with The End of Poverty. Of course, Sachs has his share of critics who aren't convinced by his arguments. Some fellow economists have suggested his sweeping reforms are too "one-size-fits-all" to be globally effective. [Image via Getty, with Tommy Hilfiger]