Probably Ceorl, although whose character is not actually in the films.
Ceorl was a messenger of Rohan during the Third Age.
Biography
Ceorl rode from the Fords of Isen with the news that Erkenbrand has been defeated. He assumes that Théoden remains in Edoras while Eomer rides to war, but is shown that he is mistaken. He joined Theoden's army, and presumably fights at Helm's Deep. His fate in that battle, and/or afterwards, is unknown.[1]
