Mummies are part of a legacy that dates back to Ancient Egypt, granted immortality by the Spell of Life. While they can be killed, they always come back after a sojourn in the Underworld; it's near-impossible, even in the World of Darkness, to finally kill a mummy once and for all. Such an ability is vital in their mission: they are warriors in the fight against Apophis, the Great Serpent, who seeks to devour existence. They also have potent Egyptian magics to assist them in their battle. That much, at least, remained constant across Mummy's various iterations.