Salman Khan
Courtesy of Khan Academy
On a typical day, Salman ("Sal") Khan pores over chemistry textbooks and biology study guides, digesting information on everything from mitosis to derivatives. But Khan, 34, isn't a pre-med student cramming for finals. He's a former hedge fund analyst who posts short video lessons (over 2,400 so far) to his free Web site,—where they help kids in dozens of countries understand everything from Hubble's Law to the French Revolution.

Khan, whose face never appears—instead, he scrawls on a chalkboard screen—started tutoring a young cousin remotely in 2004 after learning that she was struggling with math. Soon other relatives were asking him for help. When he posted a series of lessons on YouTube, they went viral, and donors like Bill Gates (who has said his kids watch the videos) offered to help him expand his efforts. In 2009 Khan quit his finance job to focus on Khan Academy; his videos have now been viewed more than 64 million times.

Khan's mission is twofold. He wants to provide the extra help or challenges kids may not be getting at public schools like the ones he attended near New Orleans (despite often "bland" instruction, he still managed to ascend to MIT and Harvard). But he also wants to reach kids who don't have access to even lackluster schools. With $2 million from Google, Khan's team is translating his videos into languages like Mandarin, Hindi, and Spanish. "The person who eventually cures cancer might be some kid in the slums of Calcutta," he says.

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