By whom is Èomer banished from the kingdom of Rohan?

Éomer is banished from the kingdom of Rohan by Gríma Wormtongue. Gríma, Théoden’s treacherous adviser, manipulates the king into distrusting Éomer and treating him as a threat.

Éomer had defied Gríma’s orders by pursuing a group of Orcs across the plains of Rohan. He also openly threatened Gríma after learning of the adviser’s interest in Éowyn. Gríma used these actions to turn Théoden against Éomer, arranging for him to be arrested and removed from Edoras.

The wording can cause confusion because Théoden is the king and formally gives the order, but Gríma is the person responsible for engineering the banishment. His influence comes from Saruman, who has encouraged him to weaken Rohan from within.

Gandalf’s arrival breaks Gríma’s hold over Théoden. Once the king is freed from his manipulation, Éomer is released, restored to honour, and becomes one of Rohan’s leading warriors. He later succeeds Théoden as king.