Saint Ciarán of Clonmacnoise, supposedly born Ciarán mac an tSaeir, was one of the Twelve Apostles of Ireland and the first abbot of Clonmacnoise. He is sometimes called Ciarán the Younger to distinguish him from the 5th-century Saint Ciarán the Elder who was bishop of Osraige. His name produced many variant spellings, including Ceran, Kieran, Queran and Queranus.

The Twelve Apostles of Ireland were twelve early Irish monastic saints of the sixth century who studied under St Finnian at his famous monastic school Clonard Abbey at Cluain-Eraird, now Clonard in County Meath.