Like Embry, his parents do not know about him being a werewolf.
Collin makes his first appearance in Eclipse when the pack goes to meet with the Cullens to train and learn about newborns in order to defeat a newborn army created by Victoria to destroy the Cullens and Bella.
During the fight against the army, he and Brady remain behind to protect the reservation under Sam's order. This is partly to protect them from harm while keeping the town safe in case some newborns went their way.
In Breaking Dawn, when the pack finds out that Bella is pregnant with a human/vampire offspring, Sam decides to take immediate action to strike the Cullens for fear of its threat. Jacob, however, refuses and runs off on his own. When Seth and Leah join him, Sam sends Jared, Paul, Quil and Collin to reason with the three to return to La Push. Jacob is curious about why Sam had sent Collin instead of Embry.
Collin makes his first appearance in Breaking Dawn - Part 1, on First Beach with the rest of his pack and the imprinted partners.
He later appears in wolf form while spying on the Cullens' house. When Emmett, Carlisle and Esme Cullen run out to hunt, he and Brady run after them, only to lose them at the ravine. He is also present when Sam goes to tell Billy Black that they may have to fight Jacob to get to Renesmee, and later participates in a fight against the Cullens until Jacob emerges to stop them.
Collin does not join Jacob's pack after everything was resolved, but remains with Sam, as one of the "pups" of the tribe.
He takes part in Alice's visionary show of force against the Volturi, standing alongside the packs, the Cullens and their allies in defense against the Volturi's "trial". In Alice's vision of the battle, Collin is shown being thrown aside by a Volturi guard, whom Paul quickly dispatches right after. He is later seen bringing down a Volturi guard with Brady's help, while Sam prepares to kill Jane.
Collin has the traditional features of a Native American; black hair, brown eyes, russet skin and is nearly 6 feet tall. In the movie, Collin is shorter than Jared, Sam, Paul, Embry and Quil.
Collin's wolf form is described as having reddish-brown fur, with his legs, face and tail being slightly darker. In the films however, he is shown to have ashy light brown fur with dark brown over his face and feet.