Chor'gorloth is an Outsider that helps with Ancient cost. He decreases the number of hero souls it costs to level ancients. This, plus Transcendent Power, will help you to easily level your ancients to high levels. Here's an example. Morgulis costs 1 hero souls per level, right? So for 100 levels he will cost 100 hero souls, right? Not anymore. With Chor'gorloth, you can level Morgulis 100 levels for less than 100 HS. And also 1000 levels for less than 1000 HS!