Nothing is known about Duke's life before the outbreak or as the outbreak began, except that he had at least one owner.
At some point after the outbreak, Duke and at least three other dogs became feral and began to travel and hunt together in a pack.
Duke is one of the hunting dogs that emerge from the woods and take Rick's group by surprise. He and the other dogs are promptly shot by a startled Sasha and cooked and eaten by the survivors shortly thereafter. Noah sees Duke's bloodied collar lying in the road and looks at it somewhat remorsefully.
After Duke appears from behind the trees with three other dogs aggressively, Sasha shoots Duke and the other dogs for food.