A question which it seems every Libertarian asks, especially if they place a great value on the works of Ayn Rand.
John Galt is a ficticious person in Atlas Shrugged, a book which Ayn Rand published in 1957.
Ayn Rand was a writer who was born in Russia, and emmigrated to the United States in 1925 being very much opposed to Communism. She was married to her husband, Frank O'Conner in 1929 and they stayed married until his death in 1979. She was a philosopher at heart, and started the Objectivism movement.
More info can be learnt about her at www.aynrand.org.