Robert de Rainault is the brother of Abbot Hugo and is the most dangerous enemy that Robin Hood has. Robert inherited the station of Sheriff from his father and since, he is Constable of a Royal Castle and has the ear of Prince John.
The Sheriff first ran across Robin Hood when it became obvious that his cousin Guy of Gisbourne could not catch Robin Hood on his own. The Sheriff has many resources available to him, so the bandits of Sherwood Forest have become his problem.
The Sheriff lusts after Marion and realizes that her heart belongs to Loxley and it goads at him unbelievably. The Sheriff believes that if he can eliminate Loxley, Marion's attention will turn to him. The Sheriff gaining Marion as a Ward has put some strife between himself and his brother the Abbott, but they still plot to bring down Loxley and his band of men.
Robert truly likes Friar Tuck, believing him to be a kindred spirit at least in the ways of wenching, however unbeknownst to him, Tuck uses his position to aid Robin and Marion's cause.
The Sheriff is an arrogant, pompous, godless, vile man. He is secure in his position and the privileges it gives him. He is given to fits of rage and has a temper several shires wide.
He is calculating and uses almost every opportunity to his advantage if at all possible. He does not look on failure kindly, unless it is his own.
The Sheriff's strongest ally is the Knight Templar Brian desBois de Gilbert. Their goals are not the same but their methods are similar.