Well-Traveled mountain clansman educated at the Citadel
Originally a member of the Stone Dogs clan of the Mountains of the Moon in the Vale, he was a lore-keeper of his clan. Thirsting for more knowledge than the mountains had to offer, he set off across Westeros to satisfy his desire for lore about the ancient history of the continent. Legends about the Dawn Age, the Children of the Forest, the Old Gods, the giants, and the coming of the First Men are his special area of interest, along with tales of the Others and the long-lost obscure magics of the world.
His quest for knowledge led him finally to Oldtown, where he stayed at The Citadel for roughly fifteen years, alternately studying and teaching. He learned a modicum of alchemy and pyromancy while there, and absorbed information on a wide variety of topics, but mostly focused on the mysteries that had first drawn him from his mountain home.
Eventually, events in Westeros gave him need to leave Oldtown. Mors Martell, Prince of Dorne, requested of The Citadel the services of a scholar who was well-versed in northern traditions and specifically the Mountain Clans of the Vale. The Citadel had no man more qualified than Haskell.