Mary

A mummified priestess and Will's foster mother. She guided him about essential day-to-day tasks. She often serves him bread which Will finds out later on was received through prayer, and eating it is an act of communion. Mary had vowed to live according to the will of Mater the earth-mother but had to make a contract with Stagnate the god of the undead in order to continue their existence in order to guard the seal of the Demon High King who Blood, Mary, and Gus failed to kill. Because of this betrayal, Mary catches fire every time she prays to Mater.

(Source: Wikipedia)