Explain Blackavar's background in Watership Down.

Blackavar's mother had not been born an Efrafan; she had come from Nutley Copse, having been taken prisoner when Woundwort attacked the warren there.  Subsequently, she had mated with an Efrafan captain, who was later killed on Wide Patrol.  Blackavar, who had looked up to his father, had once aspired to become an officer in the Owsla like him, but he had also inherited from his mother "a certain resentment against Efrafa".  These conflicting elements of his nature could not help but be recognized, and while he was praised for his courage and endurance, the "proud detachment of his nature" was also noted by his superiors.  When Blackavar was passed over for a promotion which he rightly deserved, he became convinced that the Council was prejudiced against him because of his mother's background.  He then met Hyzenthlay and became active with the "discontented does in the Right Fore".  He urged them to try to get the Council's approval to leave Efrafa, with the idea that if they did, he would go with them.  When they failed to get permission to go, he attempted to escape on his own.

Blackavar was not successful in his attempt to get away from Efrafa.  Captured by Campion, he was the victim of a cruel punishment whereby his ears were torn to ribbons, and he was kept under guard at all times.  Beaten and humiliated, Blackavar is paraded every morning and evening before the others as an example of what fate would befall any who dared try to leave the warren.  It is in this condition that Bigwig and his group find him when they come to Efrafa, and, taking pity on Blackavar, they resolve to take him with them when they leave (Chapters 35 and 40).