Ferdiad

In Irish mythology, Ferdiad (also Fer Diad, Ferdia) was the son of Daire (or son of Damáin son of Daire) and the champion of the men of Domnand (Fir Domnann) from Irrus Domnann in Connacht. Along with the Fir Bolg, the Fir Domnann were among the early inhabitants of Ireland before the coming of the Tuatha de Danaan or the Milesians. "Firdiad" means "man/warrior of the pair." ("Diad" related to dïas, or "two persons.")
See more at Wikipedia.org...

[Celtic] A hero of Irish legend who was persuaded to fight for Queen Maeve against Cuchulainn, his dearest friend. After a struggle lasting three days he was killed, to Cuchulainn's bitter grief.