Over the course of his life as a boxer, U.S. Marine, C.I.A. operative, mercenary, and costumed superhero, Marc Spector has become an expert at hand-to-hand combat techniques and various martial arts. He is an Olympic-level athlete and a skilled acrobat and gymnast, and excels as a combat strategist. He employs a variety of weapons over the course of his career, including throwing darts, nunchaku, and a truncheon. He is skilled with most weapons, and an expert with throwing weapons. He is a superb driver and can pilot a helicopter.  Taskmaster, who has the ability to copy and replicate anyone's fighting style, has stated that he prefers not to copy Moon Knight's style, as Moon Knight would rather take a punch than block it.

The son of a rabbi, Marc Spector is a former Marine and CIA operative who becomes a mercenary, despite his conflicted feelings about violence and morality. During a job in the Sudan, he is appalled by ruthless fellow mercenary Raoul Bushman. Bushman then attacks and kills archeologist Dr. Alraune. Spector saves the archeologist's daughter and colleague, Marlene Alraune, then fights and is defeated by Bushman. The dying Spector is brought into a recently unearthed tomb for shelter and placed before a statue of the Egyptian moon god Khonshu. Spector seems to die but then suddenly revives, fully healed. He claims Khonshu wants him to be the "moon's knight", redeeming his life of violence by now protecting and avenging the innocent. It is later revealed Khonshu is real, one of several entities from the Othervoid (a dimension outside normal time and space) who were worshipped as gods by ancient Earth people.

On his return to the United States, Spector invests his mercenary profits into becoming the crimefighter "Moon Knight", aided by his colleague Jean-Paul "Frenchie" DuChamp and Marlene Alraune, who becomes his lover and eventual mother of his daughter.

Along with his costumed alter ego, he uses three other identities to gain information from different social circles: billionaire businessman Steven Grant, taxicab driver Jake Lockley and suited consultant Mr. Knight. It is later revealed Marc Spector has dissociative identity disorder (incorrectly referred to as schizophrenia in some stories) and that the alters known as Grant and Lockley originally manifested during his childhood, subsequent identities emerging during his adulthood. It is debated in different stories whether Spector's mental disorder is due to childhood trauma or the result of "brain damage" caused by his psychic connection to Khonshu, a connection compelling Moon Knight's personality to shift between the four major aspects of the moon god's multi-faceted nature ("the traveler", "the pathfinder", "the embracer", and "the defender of those who travel at night"). Khonshu claims he created a psychic connection with Marc Spector when the latter was a young boy, decades before he was ready to be fully recruited as his avatar on Earth, the left Fist of Khonshu.

In most of his stories, Moon Knight has no supernatural abilities beyond occasional visions of mystical insight. He relies on athletic ability, intelligence, advanced technology, and expert combat skills. Since becoming Moon Knight, there have been multiple occasions when Marc Spector has died only to then be resurrected by Khonshu, although how many times he may be resurrected is unknown. For a time, Moon Knight's strength and resiliency to injury could reach superhuman levels depending on the phases of the moon, but this ability later vanished.

Moon Knight is an upcoming American television miniseries created by Jeremy Slater for the streaming service Disney+, based on the Marvel Comics character of the same name. It is intended to be part of the television series in the Marvel Cinematic Universe (MCU) produced by Marvel Studios, sharing continuity with the films of the franchise. Slater serves as head writer with Mohamed Diab leading the directing team.

Oscar Isaac stars as Marc Spector / Moon Knight. The series was announced in August 2019, with Slater hired in November. Diab was hired to direct four episodes of the series in October 2020, with directing duo Justin Benson and Aaron Moorhead joining the series in January 2021 to direct the other two; Isaac was confirmed to star at that time. Filming began in late April 2021 in Budapest, followed by production in Jordan, which concluded in early October before moving to Atlanta, Georgia.