Actually yeah, it was supposed to be the reward for the House of Wolves raid that never occurred, which would have presumably been Skolas, but was replaced by PoE; but it was accidentally put into one of the pre-beta exotic loot tables, so they had to add it into the vanilla game. One of the devs said that, and it's perk "Wolfpack rounds" references Skolas, also Gjallahorn is a Norse mythology derived name as is Skolas.