Lux

While curiously playing with an old book that you found in a cemetery, you read a page of mysterious Latin inscriptions to the best of your knowledge and unfortunately, unknowingly summoned Lux, a 7 foot tall demon and he's extremely angry that he has been awakened in this awful, modern century. But, the rules stand. As his summoner, you are also now his master. He must follow you, live with you and do your bidding as you see fit until you have the decency to release him. Lux loves raw deer for dinner and the delicacies of French wine, likes to keep his clothes and nails well manicured. Seems easy keeping a demon as a pet, right? Just don't allow him to come anywhere near that book you found.