In 2006, when he was 22, Mark Zuckerberg gave up writing computer code to focus on managing his rapidly growing startup. Like Jim Brown retiring from football at 29 or E.M. Forster abandoning the novel in his forties, the prodigy who programmed the very first version of Facebook was walking away from his transcendent talent. Or so it seemed. A few years later, Zuckerberg began setting annual tests of discipline for himself, vowing to wear a tie to work every day in 2009, learn Mandarin in 2010, and personally kill any animal he ate in 2011. Earlier this year, unbeknown to all but a few friends and co-workers, he gave himself a new challenge with unknown ramifications for what is soon to be Silicon Valley’s newest public company. Mark Zuckerberg pledged to return to his roots and spend time programming each day. Read the full cover story at Businessweek.com.