John Galt is a character from Ayn Rand's novel, Atlas Shrugged.

Before being introduced to the character, he's only mentioned as part of an expression. "Who is John Galt?" came to mean something along the lines of "How should I know the answer, or anyone, for that matter?"

He's basically some guy who wanted to stop the 'motor of the world,' despising how the current economic system put the producers at the mercy of consumers and the government, how they were punished for being successful.