This article considers the way in which Geoffrey Malaterra legitimizes the careers of the Hauteville family and, above all, of Roger the Great Count and his conquest of the island of Sicily. In analysing Geoffrey's relationship with Roger, which is seen as having been a close one, the author suggests that contrary to the received view that Geoffrey was a Norman, he might in fact have originally been from the region of Châteaudun or the county of Perche, and therefore was probably a protégé of Hildebert of Lavardin or Ivo of Chartres. Emphasizing that Geoffrey wrote on Roger's orders and that he was aiming to address a wide audience, the article identifies a range of qualities that Geoffrey believed made Roger and his family deserving of divine approval, focusing in particular on their heroic qualities, their innate drive to dominate, their fortitude and their eloquence. Building further on an examination of Geoffrey's use of primarily oral sources and the complex way in which he used classical and scriptural writings, the article shows how Geoffrey portrays Roger developing from his early worldly background into an agent of God's will worthy of the conferment of legatine power by Pope Urban II in 1098, the conclusion of the De rebus gestis.