Bob is a labrador that lives in Nuthanger Farm. He is present both times the rabbits come to Nuthanger Farm and caught humans attention when they tried to liberate farm rabbits.
Later in the movie he was freed by Hazel and led to Watership down during General's Woundwort's siege. He killed Efrafan rabbits, but Woundwort's body was never found. After this Bob returned to Nuthanger Farm with minor injuries.