Avens was an Efrafan officer of the Left Hind Mark along with Chervil and, eventually, Bigwig. At the end of the novel, Avens was made a captain and leads the first group of Efrafan rabbits to the new warren between Watership Down and Efrafa, Vleflain.
Avens only makes one appearance in the movie. When Hazel comes to negotiate with General Woundwort, the latter refuses. Avens than asks Woundwort if he should kill Hazel, which Woundwort denies. It is unknown what happens to him after the Battle of Watership Down.
Avens' voice actor is not present in the credits.