Óengus mac Mugróin (died 803) was a king of the Uí Failge, a Laigin people of
County Offaly. He was the son of
Mugrón mac Flainn (died 782), a previous king.[1] He ruled from 783 to 803.[2]
A conflict within the Uí Failge led to a slaughter in 789 at Cluain Ferta Mongáin (Kilclonfert, County Offaly) by Óengus at which his cousin Áed mac Tomaltaig was slain (their fathers were brothers).[3] In 803 he was treacherously killed by the followers of
Fínsnechta Cethardec mac Cellaig (died 808), over king of Leinster.[4] Finsnechta was ensuring his control of the church of Kildare which led to conflict with the Uí Failge.
His grandson Máel Sinchill mac Mugróin (died 881) was a King of the Uí Failge.