Initially dispossessed for opposing emperor Louis the Pious, Gerulf was given back his lands in 839.
Already in the beginning of his reign, Louis, in an act of grace, had returned to the Frisians what they had lost earlier in their uprisings against his father.
This act made the emperor popular among the Frisians but weakened the count's position towards the population.
In 826, he ceded a part of Frisia that was to be protected by the count of Friesland to the Danish pretender Harald Klak.
Harald got the land of Rüstringen at the left bank of the Weser to have a refuge from hostile attacks by his kin.