Grieth is the leader of the Grieth Pirates in Fire Emblem Gaiden, who kidnapped the Pegasus Knight Est. Sonya and Deen work for him, but both secretly despise him. His group of pirates and his fort are located in the eastern desert of Valentia.
Grieth has been alluded to several times throughout the story by other characters, and he makes his first physical appearance in Chapter 3: War of Deliverance through dialogue during Celica's route. He is informed of Wolff's defeat at the hands of Celica's party and orders Deen and Sonya to guard the north and south deserts respectively, plotting to deliver Celica to Rigel while apparently ending his alliance with Desaix in the process. After either of the two are dispatched and the remaining faction refuses to chase Celica's party down, the angered pirate decides to confront Celica himself with what few loyal soldiers of his remains. Despite his best efforts and the efforts of his men he is slain by Celica's party, freeing Est from his captivity, ending Deen's/Sonya's service to him, and ultimately bringing an end to his reign as the Zofian "brigand king".