In his original appearance, Imhotep was portrayed by Boris Karloff as a priest of Ancient Egypt who is mummified by pharaoh Amenhotep III as punishment for attempting to resurrect his lover, Princess Ankh-es-en-amon. Imhotep is accidentally revived when an archaeological expedition discovers his mummy and one of the archaeologists unknowingly reads an ancient life-giving spell. Imhotep escapes from the archaeologists and assumes the identity of Ardath Bey, a modern Egyptian. In this form he helps the archaeologists find the tomb of Ankh-es-en-amon. When Bey meets a woman, Helen Grosvenor, who bears a striking resemblance to Ankh-es-en-amon, he realizes that she is a reincarnation of the princess, and attempts to mummify Grosvenor and make her his bride. In the end Grosvenor, recalling her past life, appeals to the goddess Isis who causes Imhotep to be dissolved.
In the immediate sequels to the 1932 film, the mummy is known as Kharis, though this character has a back story that is very similar to Imhotep's.
In the 1999 remake, Imhotep is portrayed by Arnold Vosloo and is the main antagonist of the film. In 1290 BC, Imhotep was high priest under the rule of Pharaoh Seti I. He began an affair with Pharaoh Seti's mistress, Anck-su-namun, and they murder the Pharaoh when he discovers it. After doing so, they are discovered and Anck-su-namun commits suicide with the intention of having Imhotep resurrect her. He attempts to do so but is captured at Hamunaptra, and is punished by enduring the Curse of Hom Dai, a ritual that involved cutting out his tongue and mummifying Imhotep alive with his sarcophagus filled with carnivorous scarab beetles. As a result of the curse, Imhotep was made an undead fiend with control over sand and other elements. Three thousand years later, during an archaeological dig, Imhotep was accidentally unleashed and revived. After regenerating his body using the flesh and organs of the thieves who had opened a cursed chest, in this case an Egyptologist and three Americans, he set about trying to resurrect Anck-su-namun again, this time using Evelyn- a librarian who had discovered his body and accidentally awoken him by reading an Egyptian enchantment- for a sacrifice. Ultimately, Imhotep is defeated when his immortality is taken by the powers of the Book of Amun-Ra and he is stabbed with a sword by the film's protagonist, Rick O'Connell. As he decays back into his skeletal mummy form and falls into the pool from which he summoned Anck-su-namun's Ba, Imhotep vows to return to have his revenge, before returning to the Underworld. When he was restored to life, Imhotep gained several powers, including regeneration, invulnerability, turning himself into sand, and controlling the desert sands, as well as the ability to wield the Ten Plagues of Egypt to an unspecified degree; he was seen to turn water to blood, unleashing locusts, and control the people of the city by inflicting them with boils and sores (Although these last were used before he regained his full powers, which may account for him only using some of the plagues rather than all of them). During the first part of the movie, Imhotep expresses an intense fear of cats, screaming in fear when a white one appears in Evy's room. Ardeth Bay and Evy's superior explain that Imhotep will fear them until he is fully regenerated, cats being associated with the Guardians of the Underworld in Egyptian mythology; Rick uses this information to good effect later in the film. In the 1999 version, Ardeth Bay is not Imhotep's pseudonym, but rather the leader of an ancient secret society devoted to guarding Imhotep's tomb.
In the 2001 sequel, The Mummy Returns, Imhotep, having been resurrected and freed from the resin he had been trapped in at the end of the first movie by a group of cultists and Anck-Su-Namun's reincarnation, proceeds to seek out the Bracelet of Anubis, which was the key to finding the lair of the Scorpion King, an ancient warrior whose defeat will grant Imhotep control over the Scorpion King's near-indestructible Army of Anubis. After finding the bracelet on the arm of Alex O'Connell, the son of Rick and Evi, Imhotep captures the boy and uses him to find the lair of the Scorpion King, rejuvenating his body using the flesh of mercenaries Anck-su-namun tricks into opening the cursed chest. Once Imhotep reaches the lair, he walks over a magic seal on the floor which causes him to be robbed of his telekinesis, immortality, and other powers granted by the Curse of Hom Dai by Anubis, who seemingly wishes him to face the Scorpion King as a normal mortal. When the Scorpion King responds to Imhotep's summons, Imhotep tricks him into attacking Rick O'Connell. When Rick kills the Scorpion King and sends him and his army to the Underworld, the palace begins to collapse. Rick and Imhotep both nearly fall into a chasm, that apparently leads to the underworld, and grab onto the ledge. While Rick is rescued by Evelyn, Anck-Su-Namun leaves Imhotep to die while he begs for her assistance. After this betrayal, Imhotep loses all will to live, since his only reason for returning from the grave was to be reunited with his lover, who apparently did not love him the same. He gives Rick and Evelyn a sad envious smile and willingly casts himself into the pit, thus ending his reign of terror once and for all.