Freca attempted to force a marriage between Wulf and the daughter of King Helm Hammerhand. When Freca's plan failed, he was slain, and Wulf found himself declared the King's enemy. He fled across the borders into Dunland, where he seems to have been warmly received. For four years, Wulf built up his power in Dunland, and allied himself with Rohan's enemies.
In the year T.A. 2758, with Rohan's armies drawn into the east to repel an attack there, Wulf and his allies invaded from the west. They overran the country and took Edoras, where Wulf killed Prince Haleth; he sat in the Golden Hall and claimed the Kingship of Rohan.
The exiled King, Helm, was driven into hiding in the mountains. During the Long Winter Wulf's armies besieged him at Hornburg, and Helm's nephew, Fréaláf at Dunharrow. Helm and his second son died of the cold. In the spring, Helm was avenged by Fréaláf, who led a small party into Edoras and killed 'King' Wulf in T.A. 2759. With help from Gondor, Fréaláf cleared Wulf's followers from Rohan, and succeeded his uncle Helm to become its tenth rightful King.