The name Morgan means sea-borne in old P-Celtic. The presence of a clan Morgan in Scotland was first noted in the Book of Deer, which was written at an undetermined although very early date. They lived in Aberdeenshire and Sutherland, where the MacKays were known as Clan Morgan for awhile, and so the Morgans were classed as a Sept of Clan MacKay.
The Book of Deer emphasizes the antiquity of the Morgan family, describing how their ancestors made sacrifices to their pagan gods as well as to Christian saints. Dual religious practices were common in the very early stages of the Picts' conversion to Christianity, which began in Albann around the end of the 4th century AD.