In J.R.R. Tolkien's Middle-earth legendarium, Helm Hammerhand was the ninth King of Rohan and last King of the first line.
He became King at the death of his father Gram, during a time of crisis. His father had already fought open warfare with the Dunlendings, who operated from the captured fortress of Isengard.
Later in his reign a man named Freca appeared, a Dunlending with Rohirric blood. Freca held lands at either side of the river Adorn, the border of Rohan, and claimed to be a descendant of King Fréawine of Rohan. He planned to let his son, Wulf, marry the daughter of Helm. Freca marched to Edoras with a great force of men, planning to threathen the King to comply with his demands, but Helm Hammerhand smote him with his fist. Enraged, the men of Freca left Edoras, returning with a great force of Dunlendings. Under the leadership of Wulf they overran Rohan, but Helm withdrew in the Hornburg at Helm's Deep (which was later thus renamed in his honor), and there endured a long siege.
The Hornburg held a large war-horn, and whenever it was blown Helm would break through the Dunlending ranks, slaying many of their men. This led to a belief under the Dunlendings that the wraith of Helm Hammerhand still wandered through Rohan, and defended the Hornburg. However, at the end of the war Helm Hammerhand and his sons Haleth and Háma were slain.
He was succeeded by his nephew Fréaláf Hildeson, who defeated the Dunlendings.
