Who is John Galt?

I've been making my way through a very well-worn Atlas Shrugged (on page 188 of 1084), and Ayn Rand is blowing my mind. What an incredible writer.

Some excerpts that need no context:
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He glanced at her and did not answer. Then he said, "I like cigarettes, Miss Taggart. I like to think of fire held in a man's hand. Fire, a dangerous force, tamed at his fingertips. I often wonder about the hours when a man sits alone, watching the smoke of a cigarette, thinking. I wonder what great things have come from such hours. When a man thinks, there is a spot of fire alive in his mind - and it is proper that he should have the burning point of a cigarette as his one expression."
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"Francisco, you're some kind of very high nobility, aren't you?"

He answered, "Not yet. The reason my family has lasted for such a long time is that none of us has ever been permitted to think he is born a d'Aconia. We are expected to become one."

He pronounced his name as if he wished his listeners to be struck in the face and knighted by the sound of it.
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"Francisco, what's the most depraved type of human being?"

"A man without a purpose."
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The three of them set out every morning on adventures of their own kind. Once, an elderly professor of literature, Mrs. Taggart's friend, saw them on top of a pile in a junk yard, dismantling the carcass of an automobile. He stopped, shook his head and said to Francisco, "A young man of your position ought to spend his time in libraries, absorbing the culture of the world."

"What do you think I'm doing?" asked Francisco.
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And I just found out there's a movie coming out. The book was published in 1957, but I love that the story is timeless enough to create the film in a modern setting, 50+ years later. She was ahead of her time. I can't wait to see the movie, but I want to finish the book first.