As the King of Rohan.Théoden was growing weak with age, and was largely controlled by his chief advisor Gríma, who was secretly in the employ of the corrupt wizard Saruman. In Unfinished Tales, it is implied that Gríma was accelerating the king's decline with "subtle poisons". As Théoden sat powerless, Rohan was troubled by Orcs and Dunlendings, who operated under the will of Saruman, ruling from Isengard.
When his son Théodred was mortally wounded at a battle at the Fords of Isen, Théoden's nephew Éomer became his heir. However, Éomer was out of favour with Wormtongue, who eventually had him arrested.
When Gandalf the White and Aragorn appeared before him , Théoden initially rebuffed the wizard's advice to ride out against Saruman. When Gandalf revealed Wormtongue for what he was, however, Théoden returned to his senses. He restored his nephew, took up his sword Herugrim, and in spite of his age, led the Riders of Rohan into the Battle of the Hornburg. After this he became known as Théoden Ednew, the Renewed.
I think my next work will be in Hornburg.haha