Thesh was brought into existence when a sorcerer, studying forgotten rituals, summoned it while attempting to reach into one of the pocket dimensions of the elves. The location of the summoning was a forgotten Dwarven citadel at Faern Groht. The sorcerer who summoned Thesh, tried to bend it to his will, over time however, the sorcerer went insane, seeking more and more knowledge. finally Thesh offered him what he wanted, secrets, and that sorcerer became Thesh's first servant in this realm, transforming slowly into a Nothic.
Thesh's nothic servants tend to gather magical items, which Thesh studies for their magical properties, and occasionally will either consume their magical essence, or gift them to others to entice them into its service.
Thesh is powerful enough that it often offers to bestow a portion of its power to those who do a service for it.