Marvel Comics has secretly retconned Moon Knight's origin before he makes his MCU debut in his self-titled Disney+ show. Moon Knight is often described as Marvel's Batman, and the comparison is understandable; they're both rich men who've committed their lives to keeping the streets safe as vigilantes. But, in truth, the comparison is a far from perfect one; Moon Knight is more like Batman dialed up to 11, without a no-kill rule and with the addition of an ancient Egyptian god.
Marc Spector trained as a mercenary, but he was left for dead in the desert - where he received a vision of the Egyptian Moon God, Khonshu. He was resurrected, appointed Khonshu's fist and high priest, and returned to the world as a force for justice. Spector's experience of Khonshu has left him struggling with a supernatural version of Dissociative Identity Disorder, because - as one psychiatrist put it - his brain has been colonized by an ancient consciousness from beyond spacetime. Over the last few years, Marvel Comics has been subtly rewriting this origin story - revealing the true origin of Khonshu.
Marvel Comics has secretly revealed that Khonshu is in fact one of the Elder Gods who ruled the Earth in primeval times. Although some of the Elder Gods are benevolent entities, others such as Chthon and Shuma-Gorath learned they could increase their power by consuming their kin, and they launched a destructive war that threatened to consume the entire planet. The retcon is conducted subtly in the King in Black: Black Knight one-shot by Si Spurrier and Jesus Saiz, with Knull - a being who predates even these monstrous deities - remembering the Elder Gods, and granting Dane Whitman a vision of several of their number; Shuma-Gorath, Cyttorak, and Khonshu. Presumably Khonshu was adopted into the Egyptian pantheon, in a similar manner to Oshtur, an Elder God who became known as the Egyptian goddess Ma'at.
This was actually set up by Warren Ellis years ago. In Secret Avengers #19, he revealed the Elder Gods were also known as the "Many-Souled Ones," creatures so vast they contained multiple souls. This fits remarkably well with Ellis' portrayal of Khonshu, in which he revealed Moon Knight's Dissociative Identity Disorder is a result of his connection to Khonshu, with the multiple aspects - or "souls" - contained within him each relating to a different alter.
It's interesting to note that Marvel has secretly retconned Moon Knight's origin ahead of his MCU debut in a Disney+ TV show - one that coincides with the big-screen release of Doctor Strange in the Multiverse of Madness. Marvel has recently been attempting to synergize its Disney+ TV shows with its movies (hence Vincent D'Onofrio's debut as Kingpin in Hawkeye coming in the same week that Charlie Cox appeared in Spider-Man: No Way Home). There's already substantial evidence the Elder Gods will appear in Doctor Strange 2, so it's quite possible the MCU will use Khonshu as an Elder God as well. This latest Moon Knight retcon could be essential setup, ensuring the MCU and comic book versions are aligned.