Saint Ruain was the founder and abbot-bishop of Tallaght, a monastery in County Dublin, Ireland and a leading figure of the monastic movement known as the Celi De.
Any records that detailed Saint Ruain's life, including his birthdate or birthplace, have been long lost. His name is composed of the Old Irish Mael (one who is tonsured) and Ruain (of Ruadan). This last portion of his name likely means he was a monk of Saint Ruadan's monastery in Lothra. He is often credited with the foundation of the monastery of Tallaght during the 700s. Many of his teachings and the influence he had comes from several 9th century writings known as the Tallaght memoir. The main text is the Monastery of Tallaght which lists the precepts and habits of both Saint Mael Ruain and his associates.
The Annals of Ulster, specifically the report under the year 792, records Saint Mael Ruain's report as a peaceful one and names him both Bishop (episcopus) and Soldier of Christ (miles Christi). His successor as abbot was a monk by the name of Aireran. Today his feast day is celebrated on July 7th.