Tanin'iver is evil cosmic entity expounded in the kabbalistic teachings of Moses Cordovero and subsequent writings based on his system.
Tanin'iver is the steed of Lilith, so he is considered a mechanism by which evil is activated. Though Tanin'iver is castrated (echoing a fable about the Yetzer ha-Ra), he is still the catalyst for the coupling of Lilith with Samael, a union that brings pestilence into the world.