He was described by Amatus of Monte Cassino as "an exceptional knight, small in stature, who was very robust, strong, valiant" and by Orderic Vitalis as 'the good Norman' (French: le bon Normand).
[3] Before leaving Normandy he also donated a farm of one plough, situated at Verneuces, to the abbey of Saint-Evroul "for the redemption of the soul of his mother Emma.
[5] Richard granted his son-in-law the unconquered counties of Marsia, Campania, and Aquino as part of her dowry, giving William the title of Duke of Gaeta.
[9] William obtained some help from friends in Apulia consisting of donations and knights to support him and returned to hold Traetto against the prince.
[9] The prince in turn encamped near Traetto across the Garigliano river and for months the two sides engaged in small skirmishes.
[11] William assumed he could count on the pope opposing his master Richard, so he began burning the prince's towns.
[15] William, called le bon Normand, was in another expedition at Girona in Catalonia, Spain in charge of troops recruited from Italy and the south of France.
[16] An Islamic historian called William de Montreuil the "Captain of the Cavalry of Rome" at the Siege of Barbastro in 1063.
William gave to his cousin, Robert de Grandmesnil, former abbot of Saint-Evroul, half the town of Aquino to support him and his monks, the brothers having recently been exiled from Normandy.