Eris

Eris is the leader of the Fighters of Valoria in Ultima IX. He's a foolish coward, who turns traitor.

When the Avatar met Lambert at the city gate, Eris stood behind the bars and manipulated him into not letting the Avatar in, claiming that the Avatar worked for the Daemons. Confronting him, Eris spoke of how the Daemon Triumvirate wanted the Dagger of Valor from them, and that Eris in his cowardice was playing with the idea of simply giving it to them. Later, Lambert ignored him and allowed the Avatar entrance, and Eris was not happy about it.

When the Avatar later tried to leave the city, one of the Daemon appeared and Eris readily gave him the Sigil. From the words they exchanged, it became clear that Eris had made a deal with the Daemon. However, the Daemon simply broke his word and killed Eris anyway to prove a point.

Trivia

 * Looking into his house reveals that Eris had already packed his stuff, underlining that his giving up the Sigil was long-planned by him.