Henry Victor appears in the credits of the film as "Saxon Warrior," yet he never actually appears in the movie. The Saxon Warrior was part of a long flashback sequence showing all the heroine's past lives from ancient Egypt to the present. The sequence was cut from the final film.
A lengthy and complicated re-incarnation scene, so important to the plot, never made it into the film. This upset many people, including the film's leading actress, Zita Johann, who was a firm believer in re-incarnation.
Boris Karloff was virtually unknown when he appeared as the creature in Frankenstein. He created such a sensation that when this was made, only a year later, Universal only had to advertise "KARLOFF....'The Mummy'."
This is the only Universal monster of the time without a fictional antecedent. Large segments of the movie are scene-by-scene parallels of the movie Dracula. An ankh symbol (the ancient Egyptian glyph for "life") is substituted for the crucifix of the earlier movie. Even Edward Van Sloan's character, Dr. Muller, is quite analogous to his Dr. Van Helsing from the vampire film.
The script for this movie was originally called "Cagliostro", based on the famous French "prophet"/charlatan who claimed that he had lived for several centuries. It was then rewritten to profit from the love of all things Egyptian since the finding of King Tut's tomb, re-titled "Im-Ho-Tep", and only became "The Mummy" just before general release.
The flashback scenes in ancient Egypt were designed to resemble a silent film, with no dialog, exaggerated make-up and gestures, and a faster camera speed, to suggest the great antiquity of the events portrayed.
When Ardath Bey steals the scroll from the Egyptian Museum, he was supposed to have left powdered skin in the form of a hand-print, as he did when he escaped from his tomb after awakening when the scroll was read. The scene in which the hand-print was discovered was cut from the film, though.
Arnold Gray is in studio records/casting call lists in the role of "Knight" for this movie, but the part was almost certainly a knight in the deleted sequence depicting the reincarnations of Princess Anck-es-en-Amon prior to Helen Grosvenor. Consequently, Gray does not appear in the film as released.
The character name "Imhotep" was taken from an actual ancient Egyptian, but the real Imhotep was the architect who designed the pyramids and - far from being executed in disgrace - was the only Egyptian, other than the pharoahs, who was made a god after his death.