Howard's history of the Picts
At 13, Howard, being of Scottish-Irish descent, began his studies of Scottish history and became fascinated with what he calls "the small dark Mediterranean aborigines of Britain". As these Picts were portrayed as inferior to later tribes, Howard imagined them as a link between modern and ancient times.
His Picts originated on a group of islands in the West at the time Valusia, the kingdom of the Atlantean Kull, existed. The Picts and the barbaric Atlanteans had some kind of ancient blood feud. King Kull, however, formed a strong political link between the Pictish Isles and his kingdom of Valusia. When Atlantis, Lemuria, and Valusia sank into the sea thousands of years after Kull's time, the Picts survived and were flung into a period of cultural decline. They forgot the art of metalworking and returned to the technique of flintknapping.
Howard marks Bran as the "chief of the Cruithni Picts" suggesting that he followed the belief that the Picts once colonised Northern Ireland as well as Scotland. (cf Cruthin)
They migrated to the North until they reached Caledon, the northern lands of the later British Isles. They drove the extant tribes northward until the Aryans, Celts, and Germans invaded.
The Picts were pushed to the North, where they mingled with the tribes they had defeated earlier. Forgetting most of their technological skills, they became brutish and skilled in warcraft.
Although Bran Mak Morn has dark eyes, he doesn't resemble the Caledonian Picts as Howard depicts them. He refers to himself as a Mediterranean, possibly meaning that he associates himself with the more ancient Picts.
Following Bran Mak Morn's death, he is deified and worshipped as the "Dark Man" or "Dark One" by the Caledonians of Pictish descent. There seems to be a cult centred around him on "the Isle of Altar, near the Scottish mainland". There is a legend, similar to the idea that Ban The Blessed's severed head guards Britain from invasion, about Bran: "...mayhap we shall come to you again in your need, as Bran Mak Morn, great king of Pictdom, shall come again to his people some day in the days to come."
In "Tigers of the Sea", taking place in the time of King Arthur, Picts are one of the groups active in the turbulent British Islands in the aftermath of the Fall of Rome. In one story, they kidnap a Briton girl and intend to sacrifice her to their deity; in another, they are oppressed by Norse invaders and plan a bloody and ruthless revenge. Cormac Mac Art, Howard's Irish Viking character, alternately fights them or makes temporary alliances with them, as circumstances dictate. None of the stories set in this period makes any mention of Bran Mak Morn.
Howard's Picts still seems to be a mysterious, active fighting force during the as late as the 11th Century. They seem to be withdrawing from civilization at this time: "When the Scot Kenneth McAlpine broke the Kingdom of Galloway, the last remnant of the Pictish empire faded like snow on the mountains. Like wolves, we live now among the scattered islands, among the crags of the highlands and the dim hills of Galloway. We are a fading people."