The Complete Bran Mak Morn Trilogy

Bran is the last king of the tribal race of Picts, a mysterious, active fighting force during the Norwegian occupation of the Scottish islands as late as the 11th Century. Howard marks Bran as the "chief of the Cruithni Picts" suggesting that he followed the belief that the Picts once colonized Northern Ireland as well as Scotland.
Robert Howard (1906-1936) was an American author who wrote pulp fiction in a diverse range of genres. He is well known for his character Conan the Barbarian and is regarded as the father of the sword and sorcery subgenre.