Pedro de Montaigu was Grand Master of the Knights Templar from 1218 to 1232. He took part in the Fifth Crusade and was against the Sultan of Egypt's conditions for raising the siege of Damietta. He was Master of the French Aragon province from 1211, until his death.
A close friend of Guillaume de Chartres, it was most likely the trust the previous Grand Master had in him which meant he himself was elected so quickly in 1218. At the same time, the Grand Master of the Knights Hospitaller was Guerin de Montaigu, who is likely to have been Pedro's brother. The close relationship between the two military orders during this period was probably a result of this.
His actions against the Muslim forces working for the liberation of Jerusalem were so effective, that they were forced to propose a surrender. In return for the Templars calling off their siege at Damietta, the Islamic forces would return many Frankish soldiers, halt attacks on Jerusalem and most importantly, return the part of the True Cross, captured from the Europeans at the Battle of Hattin. Catholic pressure meant the Muslim terms were refused and the carnage continued. His military victories, aided by the Hospitaller knights, made him a renowned warrior.