Rainulf Drengot (also Ranulph, Ranulf, or Rannulf; died June 1045) was a Norman adventurer and mercenary in southern Italy. In 1030 he became the first count of Aversa. He was a member of the Drengot family.
When Rainulf was exiled by Richard II of Normandy for a violent criminal act. Rainulf, Osmond, and their brothers Gilbert Buatère, Asclettin (later count of Acerenza), and Raulf went on a pilgrimage to the shrine of the soldier-archangel, Michael, at Monte Sant'Angelo sul Gargano in the Byzantine Catepanate of Italy. They brought with them a band of 250 warriors, formed of other exiles, landless cadets and similar adventurers.
In 1017 they arrived in the Mezzogiorno, which was in a state of virtual anarchy. Establishing a stronghold at Monte Gargano in Apulia, they joined forces with the Lombard Melus of Bari, who had rebelled against his Byzantine overlords but who was currently on the run. Their first major engagement with the army of the Byzantine catepan Basil Boioannes, fought at the Battle of Cannae, an ancient Apulian villa, was a disaster for the Normans and ended in defeat. They were decimated and their leader, Rainulf's brother Gilbert, was killed. Rainulf, who now came to the fore as the undisputed leader, withdrew with the remnants of the band from Apulia to Campania, where, according to Amatus of Montecassino, though surrounded by enemies they were able to take advantage of dissension among the undisciplined Lombard lords.