That man is Ardath Bey and the tomb is of his long dead princess. The cursed priest discovers his love's spirit no longer dwells in her desiccated mummy and instead has traveled down through the ages to become Helen. They made great use of just how spooky Karloff could look, including several eerie shots of his eyes, glaring directly at the camera. Overall the only problem is that the plot seems to wander around during the middle, plus I would've loved to have seen more of Karloff as the actual mummy. Playing with the vestal virgins is a no-no.
Mummies come with their own fingerprinting kits.
English debutantes are all descendants of Egyptian royalty. Heart attacks are caused by the last priest you annoyed. Dogs hate embalmed people. Dried carcasses make great bonfires. Mummies probably spend a fortune on skin moisturizing creams.