Ceretic Guletic of Alt Clut was a king of Alt Clut (modern Dumbarton) in the fifth century. He appears in the writings of St. Patrick with the Latin name Corocticus, and this appearance in a contemporary historical source makes him the first historical king. Of Patrick's two surviving letters, one is addressed to this Corocticus, and in it Patrick lambasts the milites Coroctici ("warband of Ceretic") for his involvement with the Picts and the Scots, and for selling newly-christianized Gaels into the hands of the Picts. Ceretic's dates therefore depend on the conclusions of the vast scholarship devoted to discovering the floruit of St Patrick, but the sometime in the fifth century is probably safe. Ceretic appears also in the Harleian genealogies of the rulers of Alt Clut, from which we know his father (Cynloyp), grand-father (Cinhil) and great-grandfather (Cluim). It is from the latter source that we get his nickname, Guletic ("Land-holder"). In the Book of Armagh, he is called Coirthech rex Aloo, "Ceretic, King of the Height [of the Clyde]"
(Wikipedia)