"Rodulfe de Warenne derived his name from the hamlet of Varenne on the little river Varenne in Normandy. His parentage is unknown. He is said to have held land outside the walls of Rouen under Robert I, Duke of Normandy (died 1035), and the Cartulary of the abbey of the Holy Trinity on the Mont de Rouen proves that he held a considerable territory on both banks of the Seine upstream from Rouen. He also held land at Vascoeuil, which he gave about 1053 to the abbey of St. Pierre de Préaux, and in the pays de Caux, north of Rouen, where he sold 4 churches with tithes to the Holy Trinity in 1059, and gave another church, also with tithes, in 1074."

He married Beatrice, whose mother was almost certainly a sister of Gotmund Rufus de Vascoeuil, daughter of Tesselin, vicomté of Rouen. Keats-Rohan located a charter in which a Beatrice, seemingly identical to Rodulf's wife, is named with her sons Rodulf and Roger, and likewise shows that Beatrice was still living while a Rodulf de Warenne was marriad to Emma. Based on these (and a similar pattern of compression of generations by Robert de Torigny seen in the Montgomerys), Keats-Rohan suggested that historians were combining the records of two different Rodulfs - that Rodulf (I) married Beatrice, and by her had Rodulf (II) de Warenne and Roger de Mortimer (who by generation better fits an uncle of William anyhow), and that Rodulf (II) married Emma, having Rodulf (III, formerly II) and William de Warenne. In light of the charters she presents, this does appear the likely solution to the question.