Cúchulainn is an Irish mythological hero who appears in the stories of the Ulster Cycle, as well as in Scottish and Manx folklore. "Cú" is the Irish word for hound—"Cúchulainn" is literally "Hound of Culainn". "Cúchulainn" is technically mispronounced in the series, being closer to "coo-hullen" as audible in the following reading from Irish myths by Ronnie Drew via youtube.
The son of the god Lugh and Deichtine, sister of the king of Ulster, he was originally named Sétanta, but gained his better-known name as a child after he killed Culann's fierce guard-dog in self-defense, and offered to take its place until a replacement could be reared. At the age of seventeen he defended Ulster single-handedly against the armies of queen Medb of Connacht in the epic Táin Bó Cúailnge.
It was prophesied that his great deeds would give him everlasting fame, but that his life would be short—one reason he is compared to the Greek hero Achilles. He is known for his terrifying battle frenzy or "warp spasm", in which he becomes an unrecognizable monster who knows neither friend nor foe. He fights from his chariot, driven by his loyal charioteer Láeg, and drawn by his horses, Liath Macha and Dub Sainglend.
See Special:Whatlinkshere/Etymology:Cúchulainn for a list of articles using this term.