Éogan Már (‘the great’), according to Munster genealogical tradition, was son of Ailill Ólom (qv), a mythical king of Munster, and was the eponymous ancestor of the Éoganacht dynasties. Through a supposed liaison with Monchae the daughter of Treth, Éogan became the father of Fiachu Muillethan, whose descendants in turn allegedly included Conall Corc (qv), forefather of the Éoganacht kings. Several confused traditions, reflected in the tract ‘Cóir Anmann’ and in the genealogies, make Éogan the father of Ailill Ólom or identify him with Mug Núadat, with whom Conn Cétchathach (qv) was believed to have partitioned Ireland. The genealogists assigned Éogan two brothers: Cormac Cas (ancestor of Dál Cais) and Cian (from whom it was held that various early population groups including the Cianachta, Éile, Gailenga, and Luigni descended). Éogan Már (or Éogan Taídlech, ‘the shining one’) supposedly invaded Munster with the aid of troops from overseas to regain a kingdom that was rightfully his, but according to the tale ‘Cath Maige Mucrama’ he was later slain in that Connacht battle, in the company of Art son of Conn, by Lugaid Mac Con – a ruler of the older Érainn who had returned from banishment.
Bk Leinster, vi, 1378; O'Brien, Corpus geneal. Hib., 192, 195, 206, 362; O'Rahilly, Early Ir. myth, 184, 192; Byrne, Ir. kings, 11, 66–7, 177, 199–201; McCone, Pagan past, 110, 123, 241, 253–5; Ó hÓgáin, Myth, 182–3; T. Ó Cathasaigh, The heroic biography of Cormac mac Airt (1977), 107–27