Darth Nihilus, Lord of Hunger

Visas Marr tells her master, Darth Nihilus, about a disturbance in the Force. Darth Nihilus is a being with the ability to consume the Force itself. It makes him an embodiment of the Dark Side, but it leaves him with a constant, unending hunger to feed on the Force. This has turned Nihilus into something that is more presence than flesh. And Visas is forced to serve as his pawn.

Example of:
Evil Mentor