Robert de Sable
Robert de Sable is one of the nine people Al Mualim wants Altaïr to assassinate, and also the last of these nine. A great adversary, Robert de Sable is very good in defending himself from Altaïr's quick and deadly attacks. He is the most trained and the most greatly armored knight Altaïr faces.
Grand Master of the Knights Templar, Robert follows a goal similar to the Assassins in that he is attempting to end the war in the Holy Land. Al Mualim has no objections against him ending the Crusade but more against the way Robert De Sable attempts to do so - the Assassins would have people find peace themselves, but the Templar would force their "peace" onto others and attempt to control them. Altaïr first encounters Robert De Sable at the beginning of the game in Solomon's Temple, where he has apparently discovered the Ark of the Covenant. However, this is later revealed to be another artifact known as the Piece of Eden, which the Templar wish to use to control the minds of the people, effectively controlling those who opposed the one who held the piece. Believing that God didn't exist, he planned to bring peace and make the Holy Land a utopia by using the piece of Eden. However, since the Assassins had it, he used brutal tactics to control the people as he planned to overthrow King Richard and destroy the Assassins. When his lieutenants were assassinated by Altaïr, he convinced King Richard to ally with Saladin in order to destroy the Assassins. He was later killed in the game by Altaïr.
History
Born into a powerful family, Robert De Sable was immersed from birth into nobility. Though events during De Sable's life are difficult to pin down. At some point he became lord and ruler of Briollay, France. Subsequently, Robert De Sable entered into the order of Knights Templar and reigned as their "Grand Master" from 1191 to 1193. According to De Sable's entry on Wikipedia, "During the 3rd Crusade, de Sable and the Knights Templar laid siege to the city of Acre, which soon fell. Throughout August 1191, they also recaptured many fortresses and cities along the Palestinian coast, which had been lost previously."