Óengus the Culdee lived in the last quarter of the 8th century and is best known as the author of the "Félire Óengusso" "the Martyrology of Óengus". He founded Dísert Óengusa near Croom in AD 780. Maelruan, under whom Oengus lived, drew up a rule for the Culdees of Tallaght that prescribed their prayers, fasts, devotions, confession, and penances, but there is no evidence that this rule was widely accepted even in the other Culdean establishments. Fedelmid mac Crimthainn king of Munster (820–846) was said to have been a prominent Culdee.