Robert II (c. 1054-1134) was the Eldest son of William I (the Conqueror), succeeding him as duke of Normandy (but not on the English throne) in 1087.
His brother William II ascended the English throne, and they warred until 1096, allowing Robert to take part in the First Crusade.
When his other brother Henry I claimed the English throne in 1100, Robert contested the claim and invaded England unsuccessfully in 1101. Henry invaded Normandy in 1106, and captured Robert, who remained a prisoner in England until his death.
Why is Robert II famous?
Robert II was the Duke of Normandy from 1087 until 1106.