The series began with a homeless young newspaper seller, Billy Batson, who was confronted with a dark clothed stranger who led him down a subway station. There, a strange train appeared which carried the pair to the secret lair of the wizard Shazam. There, the ancient wizard revealed that he had selected Billy to be his champion to fight for good as the world's mightest mortal.
To that end, Shazam ordered the boy to speak his name, which was actually an acronym for various legendary figures who have agreed to grant aspects of themselves to a willing subject:
With that, Shazam immediately died and Billy vowed to fulfill his bestowed role.
Through his adventures, he soon gained a host of enemies like the mad scientist Thaddeus Bodog Sivana; a super intelligent worm called Mister Mind; an older Egyptian renegade Marvel called Black Adam; and an artificially intelligent nuclear powered robot called Mister Atom.
However, he also gained allies like a sister, Mary Batson, who could call upon the same power to become Mary Marvel (Nowadays, she prefers to be addressed as Captain Marvel herself), and a disabled friend named Freddy Freeman who could become Captain Marvel Jr. when he spoke the name of his favourite superhero, Captain Marvel (which also created the odd problem that he could not identify himself without changing). In addition, Billy met three other boys named Billy Batson (nicknamed Tall Billy, Fat Billy, and Hill Billy - the latter because he was from Appalachia {I believe}) who learned (apparently) that because they also were named Billy Batson, they could also draw on the powers of Shazam. They were known as the Lieutenant Marvels. They vowed only to use their power if asked by Captain Marvel, and only if all three were together to say the magic word, SHAZAM!". Billy also had an eccentric Uncle Dudley who claimed that he was a Marvel himself, but even though he did not, his relatives liked to humour him.
Through much of the Golden Age of Comics, Captain Marvel proved to be the most popular superhero character of the medium with his comics outselling all others, including Superman. Part of the reason for this popularity included the inherent wish fulfillment appeal of the character to children, as well as the humourous and surreal quality of the stories. This popularity was probably one reason why National Periodical Publications (now DC Comics) sued Fawcett Comics for plagarism, due to the alleged similarity of Captain Marvel to Superman. After years of litigation, Fawcett agreed to stop publication in the 1950s, feeling that a decline in the popularity of superhero comics meant that it was no longer worth continuing the fight.
When superhero comics became popular again (in what is now called the Silver Age of comic books), Fawcett was unable to revive Captain Marvel because of its earlier concession. Eventually, the characters were licensed and revived by DC Comics in the early 1970s. Because Marvel Comics had by this time established its own claim to the name Captain Marvel, DC published their book under the name Shazam!. Since then, that title has become so linked to Captain Marvel that the general public has taken to identifying the character as Shazam instead of his actual name. While the series began with a great deal of fanfare, the book got lackluster reviews and was eventually cancelled and relegated to a back story series in World's Finest.
Eventually, DC Comics bought the Fawcett line of characters, and with their mini series Crisis on Infinite Earths in the mid 1980s, fully integrated the characters into the main DC superhero setting. Since then, the characters have appeared in mini series, a graphic novel called The Power of Shazam which was followed by a relatively shortlived ongoing series. In addition, Captain Marvel was a member of the later incarnation of the Justice League while Mary Marvel and Captain Marvel Jr. had memberships in the Teen Titans. Ironically, a typical use for Captain Marvel guest appearances is to be a back up for Superman when a flying strong man is called for. As of 2003, Captain Marvel is a member of the revived Justice Society of America.
Outside comics, Captain Marvel was portrayed in the 1940 movie serial The Adventures of Captain Marvel, which is widely regarded as the best example of the form. He also appeared in the live action Saturday morning TV series Shazam!, produced by Filmation, as well as an animated series by the same company. He also was a character in the low budgeted comedy special, Legend of the Superheroes in 1978.
In the 1950s a small British Publisher, L. Miller and Son, published a number of black and white reprints of American comic books, including the Captain Marvel series. In 1954, their supply of Captain Marvel material was abruptly cut off, and they request the help of a British comic writer, Sidney Anglo, who created a British copy of the superhero called Marvelman.