Eosa (also called Ossa) is a relative amd companion of Oisc, son of Hengist. He first appears in Geoffrey of Monmouth's Historia Regum Britanniae to be in charge of the garrison at York when Oisc flees there. He is later Oisc’s partner in rebellion, replacing Ebissa in that role. In Geoffrey and Wace, Eosa is Oisc’s kinsman. According to the Cotton Cleopatra version of the Welsh Bruts, Eosa is the son of Horsa, Hengist’s deceased younger brother. Wace and Lawman make no mention of Eosa’s position at York. Instead, at this point, Wace brings in Ebissa as still Oisc’s companion.