Cummian (Cummíne, Cumméne) Foto (‘the long’) (d. 661/2) of Clonfert, was designated comarba Brénaind, coarb or successor of Brendan (qv) of Clonfert (Cluain Ferta Brénainn in some sources), Co. Galway. The genealogies give his lineage as the son of Fiachna or Fiachra, king of Munster and son of Fiachra Gairíne, a descendant of Cairpre son of Corc. Cummian belonged to Éoganacht Locha Léin of Munster. His Life contains much legendary matter surrounding his birth and other aspects of his life, chiefly alleging that he was the product of an incestuous union of Fiachna and his daughter. He was a student of Colmán (qv) of the moccu Chluasaig of Cork, who wrote a lament for him.
It is known that Clonfert had connections with Iona and its dependent monasteries going back to the time of Brendan. For this and other reasons, it is probable that Cummian is the author of the Paschal letter of 632 addressed to Ségéne (qv) (d. 652), 5th abbot of Iona, and one Beccán ‘the hermit’. It concerns the controversy that had arisen within the Irish church over conflicting systems used in calculating the date of Easter. Pope Honorius had sent a letter to the Irish churches (628/9), urging them to abandon their traditional observance of an Easter cycle which differed from that of the rest of the western church. Following a synod at Mag Léne (near Durrow, Co. Offaly) around 630, some of the Irish churches agreed to celebrate Easter the following year at the same time as the universal church. Discord subsequently arose, however, so envoys were sent to Rome to consult the pope. It appears that soon after their return Cummian wrote his Paschal letter (the only one of its kind to survive from the early Irish church) arguing that Iona and its vast paruchia should conform with the rest of Christendom. The letter shows Cummian as a learned man with a knowledge of a wide range of patristic material, and familiarity with no less than ten Paschal cycles.
Cummian is also credited with the authorship of the hymn ‘Celebra Iuda’ and (with some probability) of a systematic penitential based on the eight deadly sins. His name is associated with a series of lists giving descriptions of Christ and the apostles, which shows familarity with Roman iconographic material. He may also be the author of an extant commentary on the gospel of Mark. The Annals of the Four Masters record the translation of his relics to a shrine in Clonfert in 1162.