The Greek mythographer Euhemerus originated the concept of Euhemerism, which treats mythological accounts as a reflection of actual historical events shaped by retelling and traditional mores. In the 12th century, Icelandic bard and historian Snorri Sturluson proposed that the Norse gods were originally historical war leaders and kings, who later became cult figures, eventually set into society as gods. This view is in agreement with Irish historians such as T. F. O'Rahilly and Francis John Byrne; the early chapters of their respective books, "Early Irish history and mythology" (reprinted 2004) and "Irish Kings and High-Kings" (3rd revised edition, 2001), deal in depth with the origins and status of many Irish ancestral deities.