Robert Curthose was the eldest son of William the Conqueror. Usually when a king dies, his eldest son would become king, but after a disastrous relationship with his father and brothers, he only got the Duchy of Normandy. His younger brother William got the throne of England instead but later died (probably murdered) and his brother Henry became king. Henry and Robert quarreled and Robert was defeated and imprisoned by Henry when he was 55 until he died in his early eighties.