Collin is one of the youngest members of Sam Uley's pack.
During the fight with Victoria's army in Eclipse, he and Brady remained behind to protect the reservation. He also took part in the show of force against the Volturi during Breaking Dawn. Collin did not join Jacob's pack, but remained with Sam Uley, as one of the "pups" of the tribe. In Breaking Dawn, it was mentioned that, like Embry, his parents do not know about him being a werewolf.
Collin, along with Brady, are the only members of the pack who've never been seen in their human forms. They do not appear in the movies.