Fawcett Comics, a division of Fawcett Publications, was one of several successful comic book publishers during the Golden Age of Comic Books in the 1940s. Its most popular character was Captain Marvel, the alter ego of boy radio reporter Billy Batson, who transformed into the hero whenever he said the magic word "Shazam!" Other characters published by Fawcett include Captain Video, Hopalong Cassidy, Ibis the Invincible, Bulletman and Bulletgirl, Spy Smasher, Captain Midnight, Phantom Eagle, Mister Scarlet and Pinky, Minute-Man, Commando Yank and Golden Arrow.
The whimsical adventures of Captain Marvel and the Marvel Family (which included Captain Marvel Jr., Mary Marvel, the Lieutenants Marvel, et al.) eventually outsold those of Superman. National Comics (as DC Comics was then known) sued Fawcett, claiming that the Captain infringed on the copyright of its original costumed superhero. National Periodical's 1941 copyright hearing against Fawcett was dismissed on a technicality; National had failed to secure the copyright to the Superman newspaper strip.
Facing a declining comics market and with their other divisions flourishing, particularly the flagship Mechanix Illustrated which had struck gold with Tom McCahill's new-car road tests (the first to appear in an American publication), in 1953 Fawcett Comics ceased publication of its superhero titles and settled the ongoing case. Astonishingly after having spent a full decade in court over the copyrights, neither National nor Fawcett insisted on provisions to keep the trademarks active so that nobody else could start calling their comics "Marvel". Several of Fawcett's completed stories and artwork, as well as a few characters, were sold to Charlton Comics. Fawcett returned to publishing comics in the 1960s, but mainly to publish Dennis the Menace (US) and other books of reprinted Newspaper Comics.
In the late 1960s Marvel Comics gained the trademark "Captain Marvel" with its first series. In 1972 DC licensed and in 1994, purchased Captain Marvel and his related characters. Because of Marvel's trademark, DC has instead used the trademark Shazam! as the title of its Captain Marvel-related comic books and thus the name under which it markets and promotes the character. In 1973, Shazam and the Marvel family became an additional Earth (to the pre-Crisis DC continuity), known for a period of time as Earth-S.
However, all of the Fawcett characters in their original 1940s incarnations in the issues in which they appeared are in the Public Domain. Any changes added by DC or any other company are protected under that company's copyright and cannot be used freely or without permission.