Cosa, Ebissa, Eisc, Osa, Ossa, Oysa, Tosa
A cousin or son of the Saxon leader Hengist. Hengist brought him to England with Octa and other Saxon warriors when Vortigern, King of Britain, was friendly to the Saxons. The Saxons eventually went to war with the British, and Eosa and Octa became their leaders.
King Ambrosius defeated Eosa at the battle of York and – as a peace offering – gave him a section of Scotland. Eosa and Octa returned, however, to fight Uther after Ambrosius’s death. Uther captured them at the battle of Mount Damen and imprisoned them, but they escaped to Germany, raised an army, and returned again. The two Saxons were finally killed at the battle of Saint Albans (or Verulam).
Eosa is probably identical to the son of Hengist mentioned by the Anglo-Saxon Chronicle as Æsc. Wace gives two versions of his name – Ebissa and Osa – which Layamon understood as two separate characters.
Sources
Historia Brittonum | Probably Nennius, early 9th century
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
Roman de Brut | Wace, c. 1155
Brut | Layamon, late 12th century to mid-13th century