Battle of the Pelennor Fields
In "The Return of the King", Théoden led the Rohirrim to the aid of Gondor at the Battle of the Pelennor Fields. In that battle, he routed the Harad cavalry, personally killing their chieftain. He challenged the Witch-king of Angmar, the leader of the Nazgûl, but was mortally wounded when his own horse Snowmane fell upon him. He was avenged by his niece Éowyn and a hobbit, Merry Brandybuck, who had ridden to war together in secret; together, they destroyed the witch-king. In his last moments, Théoden bade farewell to Merry and Éomer.