This is given by Hobart as the reward for the Quest to defeat Overlord Gninkan.
Most interestingly, on a Monk, this, and the rest of the Gloomleather set, appears as the Velious Monk texture, not as plain leather.
Human Druid, Old models, Gloomleather Tunic & Pants
Human Monk, Old models, Gloomleather Tunic & Pants, Original textures
Human Monk, Old models, Gloomleather Tunic & Pants, Velious textures
Human Druid, Luclin models, Gloomleather Tunic & Pants
Human Monk, Luclin models, Gloomleather Tunic & Pants