Paul is basically some poor soul who happens to become a werewolf (what a pity). He hates Bella and crew because they are a bunch of wussies and Mary Sues, so in short, he's really one of the best characters in the Twilight Series. He also cannot stand Jacob, and is always trying to eat him.
We first see Paul in New Moon, when Jacob is telling Bella how scared he is of Sam Uley and company. Paul and his bud Jared are the first to turn wolf and they follow Sam around like little ducklings. In Eclipse he has a somewhat greater role, as he is in the totally awesome fight...that no one saw happen... damn. Anyway he seems to have some kind of anger problem, as he frequently fursplodes into a hairy grey beast. In Mopey Crapfest 2 he almost ripped Bella's face off when she slapped him upside the head. Can't say I blame him. You'd rip someone's face off too if you were stuck in this
saga garbage pile.
In Breeding Spawn Paul imprints on Jacob's sister Rachel. Then he spends most of his time eating all of the Blacks' food. Imprinting seems to have solved his anger problem, as he is now happy as a clam, even when Jacob punches him and breaks his nose just because Jacob's so fed up with this annoying jackass eating all his chips. When Jacob runs off to make his own pack, Paul stays with Sam, and alas, we hear no more of him, because all potentially good characters in Meyerland disappear, never to be heard from again.