DC Comics started out as three separate companies — National Allied Publications, founded by Major Malcolm Wheeler-Nicholson; Detective Comics, Inc., founded by Harry Donenfeld and J.S. Liebowitz; and All-American Publications, founded by M.C. Gaines, who had earlier packaged comic books for Dell Comics. Nicholson and the Donenfeld/Liebowitz company formed a partnership in 1936, and in '37, the latter bought Nicholson out. The resulting company was officially named National Comics (later National Periodical Publications), but used "DC", which stood for "Detective Comics", in its logo.

Gaines's All-American Publications shared offices with DC starting in 1938, and its comics, too, appeared under the DC logo. But it remained a separate corporate entity for years, although the two cross-promoted each other's titles and characters sometimes passed between them. In 1944, the two briefly separated, and an "AA" logo appeared on the All-American titles. But in '45, Gaines sold most of his existing titles to DC, and went off to found EC Comics.

DC's comics included Action Comics, Detective Comics, Star-Spangled Comics, Adventure Comics, More Fun Comics, Leading Comics, World's Finest Comics, All Funny Comics, and all their offshoots. All-American's titles were All-American Comics, Flash Comics, All Star Comics, Sensation Comics, Funny Stuff, Comic Cavalcade, and their offshoots.

DC was not only the first to publish superheroes — it was also prominent among the companies exploiting the trend. By the early 1940s, not just Superman, but also Batman, The Flash, Green Lantern, and Wonder Woman were appearing in their own comics; and the anthology titles were also dominated by that genre. Even Funny Stuff featured a costumed, super-powered turtle called The Terrific Whatzit, and All Funny's Genius Jones often appeared in costume as "Answer Man".

In 1940, DC brought several of its characters together as The Justice Society of America — another first — which contained four characters from DC comics and four All-American ones. (The JSA itself appeared in an All-American title, and temporarily dropped the DC characters during the 1945-46 split.) DC was also the first to publish a Justice Society imitation — The Seven Soldiers of Victory ran in Leading Comics from 1941-45.

During the late 1940s, superheroes fell out of favor. Leading Comics and Comic Cavalcade converted to funny animals, More Fun to general humor, All-American and All Star to western, Sensation to mystery, and Star-Spangled to war stories, while Flash ceased entirely. In the '50s, DC also published science fiction, spy stories, teenage humor, romance, and even celebrity vehicles — Pat Boone, Bob Hope and several other stars appeared in their own regularly-published DC comics. Unlike most comics publishers, however, DC never put out the sort of gruesome horror and crime comics that brought on the protest that led to the formation of the Comics Code Authority.

Just as it had led the way in the original superhero trend, DC led in their revival. A new Flash in 1956 and a new Green Lantern in 1959 paved the way for a wholesale revival of the genre in the early 1960s. Before long, the '50s variety show had been buried under the likes of Metamorpho, Hawkman, Doom Patrol, Ultra the Multi-Alien and, of course, The Justice League of America. Before long, as in the early '40s, practically everybody that published comics, published superheroes. Since then, the intensity of that genre's domination of the comics market has waxed and waned to a certain extent, but there has never been any doubt that superheroes dominated the market.

In 1956, Quality Comics went out of business, and DC acquired its assets. That made Blackhawk, Plastic Man and quite a few other characters DC properties. In 1967, Dick Giordano, who had formerly been chief editor of Charlton Comics, moved to DC. He was instrumental in engineering a 1983 deal whereby DC acquired all of Charlton's superheroes, such as Captain Atom and The Blue Beetle. In 1973, DC licensed Captain Marvel and his associated characters from Fawcett Publications. Later, it bought those characters, and all the rest of Fawcett's superheroes, such as Spy Smasher and Bulletman, outright.