Vilkas is a member of the companions.
In the episode, S'oggy Balls (Episode), S'oggy Balls meets Vilkas and Kodlak when he asks if he can join the Companions. Kodlak asks Vilkas to test his skill and S'oggy K.O.s Vilkas in the balls. 30 minutes later, Vilkas wakes up and tells Kodlak that he is ready to join the Companions.Later, Vilkas gives S'oggy a new mission to save a Whiterun citizen named Gwendalyn. (A Little CatDog)
In the episode, Turkey Time, it is revealed that Vilkas wears a "traveling hat" when he ventures out of Whiterun. He and S'oggy are out to get revenge on the Silver Hand Clan for killing Kodlak, their former leader. (Wuuthrad)