Helm was physically a strong king and a fierce
warrior. Despite this,
a man named Freca, who claimed descent from Frëawine, caused
unrest in Rohan. His son, Wulf, then led an
invasion of Dunlendings at the same time as the Corsairs of Umbar
attacked. The Mark was completely overrun and Helm fled to the
Hornburg where he died after a brave but useless charge.
Both his sons also perished during the war and the winter that followed, so the crown passed to Fréaláf, Helm's sister's son. Helm's sister's name was Hilde.
References: Unfinished Tales, Lord of the Rings,
Tolkien Quiz Book
Helm, son of Gram,
was succeeded by his sister's son, Fréaláf.