Santa was most likely a Viking back in his hey-day. He was blessed by some Norse god so whatever he rode could fly. Taking advantage of this, he pillaged the hell out of the nearby towns, amassing a wealthy horde unlike any other. He collected precious metals, legendary artifacts, and virgins, bestowing him immortality as well as all the pleasures the world could offer. He kept this up for a good while, though he had to move his base of operations from Norway further up north—as north as anyone could go. Otherwise he would most likely get killed in his sleep. It explains why he doesn't use the South Pole.
Anyway, nowadays he just sits around, going out of his way every once in a while to give away some of the valuable junk he's collected over the years to clear up space.