Eochaid Mugmedon ("slave-lord") was a semi-historical High King of Ireland of the 4th century who was said to be the ancestor of many of Ireland's most significant dynasties, such as the Connachta and the Uí Néill.

By his wife, Mongfind, he had sons Brion, Ailill and Fiachrae. By a slave he captured on a raid in Britain, Cairenn, he had a fourth son, Niall, later known as Niall Noigiallach (Niall of the Nine Hostages).