Cadfan (Latin: Catamanus), was the 6th century founder-abbot of Tywyn (whose church is dedicated to him) and Bardsey, both in Gwynedd, Wales.
He was said to have received the island of Bardsey from Einion Frenin, king of Llŷn, around 516 and to have served as its abbot until 542.
He journeyed to Britain accompanied by the children of Ithel Hael o Lydaw (of Brittany): Baglan, Flewyn, Gredifael, Tanwg, Twrog, Tegai, Trillo, Tecwyn and Llechid.
Wade-Evans thought Kentinlau, who accompanied Cadfan to Ceredigion, should be identified with Cynllo.
He also established a clas at Tywyn (traditionally the first such clas in Wales) which became a wealthy site, served by an abbot and clerics from 1147 to 1291, mother church of the cantref of Meirionnydd south of the River Dysynni.