He was raised as a Cathar but eventually converted to Catholicism in a move that would help restore peace to his homeland following the ravages of the Albigensian Crusade.
Olivier was the son of Raymond de Termes, count of the Termes region of the Carcassonne district, then lying on the border between Languedoc and Catalonia.
The region was overwhelmingly Cathar in religion, and Oliver's father was besieged by Simon de Montfort in his castle at Chateau de Termes in 1210.
Having survived the fall of the castle, Oliver made his way south with other refugees from the crusade to the court of Aragon, where he befriended the future King James I of Aragon.
He spent much of the remainder of his life assisting in military operations in the Holy Land (participating in both the Seventh Crusade and Eighth Crusade), advising the king, and helping pacify Languedoc.