Geoffrey de Rancon was a French army commander that lived in the 12th century. He served as Eleanor of Aquitaine's army commander during the Second Crusade. When the Crusaders, led by King Louis VII of France (Eleanor's consort) climbed Mount Cadmos, Rancon disobeyed orders and chose to march further than the spot chosen by the King for camp. He decided in concert with the Count of Maurienne (Louis´ uncle), that a nearby plateau would make a better camp, but such disobedience was reportedly common in the army, due to the lack of command from the King. As a result, the army was split and disorganized, and the Turks successfully ambushed a portion. The King narrowly escaped, and the blame for the massacre fell on Rancon.
King Louis sent Rancon home from the Crusade early, as a punishment. In the novel, The Book of Eleanor, by Pamela Kaufman, he is renamed Richard of Rancon, and is Eleanor's lover. However, there is no historical evidence that this was in fact the case.
A descendent of Rancon was married to Isabelle, the daughter of Eleanor's daughter in law Isabella of Angoulême.