Captain Marvel, also known as Shazam (), is a fictional superhero appearing in American comic books published by DC Comics. Artist C. C. Beck and writer Bill Parker created the character in 1939. Captain Marvel first appeared in Whiz Comics #2 (cover-dated Feb. 1940), published by Fawcett Comics.

After the success of National Comics' new superhero characters Superman and Batman, Fawcett Publications started its own comics division in 1939, recruiting writer Bill Parker to create several hero characters for the first title in their line, tentatively titled Flash Comics. Besides penning stories featuring Ibis the Invincible, Spy Smasher, Golden Arrow, Lance O'Casey, Scoop Smith, and Dan Dare for the new book, Parker also wrote a story about a team of six superheroes, each possessing a special power granted to them by a mythological figure.  Fawcett Comics' executive director Ralph Daigh decided it would be best to combine the team of six into one hero who would embody all six powers. Parker responded by creating a character he called "Captain Thunder". Staff artist Charles Clarence "C. C." Beck was recruited to design and illustrate Parker's story, rendering it in a direct, somewhat cartoony style that became his trademark. "When Bill Parker and I went to work on Fawcett's first comic book in late 1939, we both saw how poorly written and illustrated the superhero comic books were," Beck told an interviewer. "We decided to give our reader a real comic book, drawn in comic-strip style and telling an imaginative story, based not on the hackneyed formulas of the pulp magazine, but going back to the old folk-tales and myths of classic times".  The first issue of the comic book, printed as both Flash Comics #1 and Thrill Comics #1, had a low-print run in the fall of 1939 as an ashcan copy created for advertising and trademark purposes. Shortly after its printing, however, Fawcett found it could not trademark "Captain Thunder", "Flash Comics", or "Thrill Comics", because all three names were already in use. Consequently, the book was renamed Whiz Comics, and Fawcett artist Pete Costanza suggested changing Captain Thunder's name to "Captain Marvelous", which the editors shortened to "Captain Marvel". The word balloons in the story were re-lettered to label the hero of the main story as "Captain Marvel". Whiz Comics #2 (cover-dated Feb. 1940) was published in late 1939. Answer this question using a quote from the following article:

how were they in use?
Shortly after its printing, however, Fawcett found it could not trademark "Captain Thunder", "Flash Comics", or "Thrill Comics", because all three