Gisulf was the son of Romuald II of Benevento and Gumperga, daughter of Aurona, sister of Liutprand. As a relative of the king, he was supported by the royal power, but being a minor on his father's death, one Audelais managed to usurp the duchy. Liutprand removed Audelais and, placing another nephew, Gregory, on the throne, brought Gisulf back to be raised in the royal palace at Pavia.
The Beneventans (or Samnites) remained faithful to Gisulf and his father's dynasty, however, and when, after Gregory's death, Godescalc usurped the ducal throne, the people rose up and murdered him, allowing Liutprand to place the now-adult Gisulf in power. According to Hartmann , Gisulf followed the policies of Liutprand faithfully.
↑The Lexikon gives a date of 741 and places the death of Gregory there, making him succeed, not Godescalc, but Gregory. The length of ten years comes from Hodgkin.