abbot who was one of the most illustrious founders of monasticism in Ireland.

With Saints Columba and Brendan, Ciaran was educated by Abbot St. Finnian at the celebrated Monastery of Clonard. From there he went to the island of Aranmore, in Galway, off the western coast of Ireland, where he became the most famous disciple of Abbot St. Enda. Ciaran later traveled to central Ireland, visited several monasteries, and settled with eight companions at Clonmacnoise, where in 548 he founded an abbey that subsequently developed into one of the most famous Irish monastic cities; by the 9th century it was a great centre of learning. So influential was Ciaran's establishment that more than half the monasteries in Ireland reportedly followed its severely ascetic rule, traditionally attributed to Ciaran.

There is an annual pilgrimage to Clonmacnoise on Ciaran's feast day. His four extant biographies record his numerous alleged miracles. Ciaran's holiness and monastic activity led to his being ranked among the Twelve Apostles of Ireland. He has often been confused with the 5th/6th-century St. Ciaran of Saighir (designated “the Elder” or sometimes called “of Ossory”), who is traditionally honoured as Ossory's first bishop.