KENTIGERN (whom the Scots on account of the sweetness of ways called Mungo, that is, Dearly-Beloved) is said to have been the grandson of King Loth, (from whom is named that part of Scotland known as the Lothians.) in which case he was of the royal stock of the Picts in North Britain. In boyhood he was given over to the Monastery of Culross, under the tutelage of its bishop and Abbot Saint Serf; from whose teaching he made headway in the study of letters, and also in the things of God. Hence he later withdrew into a solitary place at Glasgow in Scotland, where he lead a hard life, in constant meditation upon the things of heaven, until the faithful of those parts, moved by the fame of his holiness, duly chose him for their bishop.
WHEN he had been raised to the dignity of the episcopate, he forthwith shed around the bright rays of apostolic grace, like a candle set upon a candlestick. By his words and his example he so tended his flock that many were in such wise enkindled with the love of Jesus Christ as to keep nothing of their own, but to serve God with one heart and one mind like the first disciples of the Apostles. Kentigern himself relaxed nothing of the first way of his life. It was his use every day, besides other works of godliness and penance, to repeat the entire Psalter; and every year, after the example of Christ, he passed in the desert the whole time of the fast of forty days, cut off altogether from the conversation of men.
GOD confirmed his preaching with many and great miracles ; and thus this holy bishop, mighty in word and in work, preserved his flock unhurt from the Pelagian heresy which crept all round about. And in his vast diocese, whereabouts he travelled many times on foot, he almost abolished the worship of false gods, and brought a countless multitude of heathen into the Church of Christ. With this, nevertheless, he was not content, but sent churchmen meet to preach the Gospel into northern Norway and Iceland. And he lacked not the merit of suffering hardship for Christ's sake ; for he was driven into exile by a wicked tyrant, and betook himself to Wales, where he dwelt for a while with Saint David the Bishop ; and there he is said by some historians to have founded, at the confluence of the -Elwy and Clwyd, a famous monastery, where he trained up Saint Asaph as his disciple. About the year 603 he went to heaven, full of days and beloved of God and men. His body was buried in the Cathedral Church of Glasgow, where it was held in great honour until the times when the fury of the Calvinistic heresy well nigh exterminated Catholic belief from Scotland.
--from The Anglican Breviary