The Uí Fiachrach were a dynasty who originated in, and whose descendants later ruled, the coicead or fifth of Connacht (a western province of Ireland) at different times from the mid-first millennium onwards. They claimed descent from Fiachrae, an older half-brother of Niall Noigiallach or Niall of the Nine Hostages. Fiachrae and his two full brothers, Brion and Ailill, were the collective ancestors of the Connachta dynasty that eventually became the new name of the province. Their mother was Mongfind.