Mary Marvel is a fictional character, a superhero derived from the DC Comics (formerly Fawcett Comics) character Captain Marvel. Her alter ego is fourteen-year-old Mary Batson, twin sister of Captain Marvel's alter ego Billy Batson. Like her brother, Mary has been granted the power of Shazam, and has but to speak his name to be transformed into the superpowered Mary Marvel.

Mary Batson was separated from her brother Billy after their parents died in a car accident, and raised as Mary Bromfield. Years later, the siblings were reunited, Billy having since become Captain Marvel, but Mary was subsequently kidnapped for ransom. During the course of rescuing her, Captain Marvel and Captain Marvel Jr. were incapactitated, but fortunately for all, Mary discovered that saying the magic word "Shazam!" would transform her as it did her brother, only she remains at her current age.

Mary Marvel, like Captain Marvel, receives her powers from the gifts of various gods and legendary figures by speaking the magic word "Shazam":

S for Selena for grace

H for Hippolyta for strength

A for Ariadne for skill

Z for Zephyrus for fleetness (and flight)

A for Aurora for beauty

M for Minerva for wisdom

Althoug these deities were originally stated to be the goddesses who served as counterparts to Billy's patrons, it should be noted that Zephyrus is a male god, and that the list does not account for all of the superhuman traits shared by Billy and Mary. When Mary was given a new (but similar) origin in The Power of Shazam!, she gained the same powers as Billy, from the same sources.

After the Marvel Family's adventures ceased publication in 1953, Mary Marvel went unseen for years. In the early 1970s, DC Comics bought the rights to the Marvels, and revived them in a series called Shazam!. In recent years, as seen in the 1990s comic series Power of Shazam!, Mary becomes an adult woman upon saying the magic word, and wears a white version of her original costume. An underlying story theme in that series involved the romantic conection between Mary and her teammate, Captain Marvel, Jr. (Freddy Freeman), much to her brother's distaste.

The current version of Mary Marvel sometimes also refers to herself as "Captain Marvel"; since she draws from the same powers as her brother, she is also entitled to the name as well. Power of Shazam! writer Jerry Ordway was among the few writers to call Mary "Captain", and differentiated her from her brother by referring to Mary as "the lady Captain Marvel" or "Captain Marvel II". Most other writers continue to refer to the character as "Mary Marvel"; for example in the Formerly Known as the Justice League miniseries, in which she became an official member of the Justice League.