From The Lord of the Rings wiki
King Theoden
King Theoden was the seventeenth King of Rohan who led his people during the War of the Ring, famously breaking the influence of Saruman before falling in the Battle of the Pelennor Fields.
Reign and Corruption
Theoden was the ruler of the Mark of Rohan, a kingdom of horse-lords in Middle-earth. For a significant period, he was manipulated by his advisor Grima Wormtongue, who was secretly in the service of the wizard Saruman. This influence left Theoden in a state of lethargy and decay, weakening his realm as the threat of Mordor grew. He was eventually liberated from this malaise by the intervention of Gandalf the Grey, who restored the king to his rightful senses.
War of the Ring
Following his recovery, Theoden proved himself a valiant warrior and leader. He successfully defended his people at the Battle of Helm's Deep and later honoured an ancient alliance by leading the Rohirrim to the aid of Gondor. During the Battle of the Pelennor Fields, he fought alongside companions such as Aragorn, Gimli, and Legolas Greenleaf. Theoden met his end on the battlefield while charging the forces of the Witch-king of Angmar, dying as a hero who restored the honour and strength of his line.
