Gerolf or Gerulf (Old Dutch: Gērulf; c. 850 – 895/896) was the second count of this name who is attested in the area of Friesland (which also included Holland at the time).
His ancestry is unclear, but he may have been a son or, more likely, a grandson of the earlier Gerolf, who was a count in the area of Frisia at the time of the reign of Emperor Louis the Pious (fl.
There is some limited and vague evidence that this earlier Gerolf was a son of a certain Theodoric, who in turn supposedly descended from the Frisian king Redbad (d. 719).
It was not until 885 that this situation was put to an end by the murder of Godfrid, Duke of Frisia at a place called Herespich (identified as modern Spijk).
It might be important remembering, in face of this scenario, how Merovingian and, most particularly, Carolingian leaders had hunted heathen Frisians just before the Frankish society had to deal with the Viking expansion.
In this sense, it is interesting, as well, to observe how far the Gerulfingian House of Holland, during the centuries to follow, would pose an obstacle for the full grasp of this region by the Holy Roman Empire.
This prince Radboud fell in battle in 874, while repelling a Viking incursion together with Reginar "Longneck" (Count of Maasgau, later Duke of Lorraine).
It is further speculated that because Gerolf's sister may have been Dirk and Waldger's mother, her brother acted as her children's guardian after their father had been killed.