According to a Latin
Life of Deiniol, preserved in Peniarth MS226 and transcribed in 1602 by Sir Thomas Williams of Trefriw, he was the son of Abbot
Dunod Fawr, son of
Pabo Post Prydain. The family, having lost their land in the
North of England, were given land by the king of
Powys,
Cyngen Glodrydd. Deiniol embraced the religious life and is said to have studied under
Cadoc of
Llancarfan. Sir David Trevor describes Deiniol as one of the seven blessed cousins who had spent part of his early life as a hermit "on the arm of Pembrokeshire" but was called to be a bishop despite deficiencies in his formal education. Deiniol soon left Powys for Gwynedd where he founded the monastery of
Bangor, Gwynedd under the patronage of
Maelgwn Gwynedd who endowed it with lands and privileges, later raising it to the rank of the official seat of a bishop, sharing a common boundary with the principality of Gwynedd. Deiniol is said to have been consecrated to that See by St.
Dubricius in the year 516. Deiniol spent the remainder of his days there as Abbot and Bishop. He attended the
Synod of Llanddewi Brefi in c. 545 with
Saint David when the subject of rules for penance was being discussed. According to the
Annales Cambriae Deiniol died in 584 and was buried on
Bardsey Island. It is possible that this date, like the dates given for the deaths of David and Kentigern, is twelve years later than it should be, in which case the correct date is 572.
The Cathedral Church of Saint Deiniol in Bangor is dedicated in his name. ==Legacy==