So there is some Cosmic Being locked away so that it cannot interfere with the outside world. Some sort of powerful being... Good, Evil, or neither, it doesn't matter. But this time, they didn't lock away the being in a magical jar of some sort. Rather, they somehow managed to bind the thing into the body of a person. A person who may, or may not be aware that they are carrying around some Eldritch God within them. A Subtrope of Sealed Evil in a Can, Sealed Good in a Can, and Sealed Badass in a Can. Contrast Grand Theft Me. Compare Treasure Chest Cavity.