Arnold went from a caged Rottweiler that most of the Entourage clan was afraid of in his first appearance, to an integral background character on the show that was almost more popular than his human co-stars. The writers didn't use Arnold as often in the plots of the shows as others on this list, which made him seem like a real dog rather than a gimmicky cast member. He just hung out with his owners, slobbered a bit, and was occasionally used to pick up women at the local park. He was the ultimate accessory for the sex-crazed characters on the show.