The time between The Golden Age of Comic Books and The Silver Age of Comic Books. Superheroes were at their lowest ebb here; the end of World War II meant that people were tired of hearing about individuals fighting to save the world, and other genres of comic book took over — horror, crime, Funny Animals, and so on.
By the end, only a few superhero comics were still going, Batman, Superman, Superboy and Wonder Woman chief among them. Plastic Man was the last non-DC superhero left before being bought out. Apart from a few scattered and failed attempts at revivals such as Atlas Comics' Captain America (which was later retconned in the 1970s as the adventures of an imposter soon driven insane by a flawed copy of Project: Rebirth) and Sub-Mariner, and Jack Kirby and Joe Simon's disguised attempt with Fighting American and Stunt Man, the genre seemed to have no life in it. However, they did kickstart the romance comic genre with Young Romance, which proved a big success.
The big exception to the general lack of interest in superheroes was Superman, whose popularity was healthy enough that his franchise actually expanded in 1954 when his supporting character Jimmy Olsen was spun off into a comic of his own. The reason Superman did so well was probably thanks to the much loved TV show The Adventures of Superman with George Reeves which kept the Last Son of Krypton in the public eye even among non comic readers.
This was the era when The Comics Code was enacted, and it may have been what ultimately brought superheroes back. Though the hearings that led to it put some of the blame on superheroes, they were especially unkind to crime and horror, and those genres were pretty much gutted by the Code. Meanwhile, superheroes were easy enough to retool to follow the Code, and experienced a resurgence in popularity that led to The Silver Age of Comic Books.
The end of the age is pegged at different points, depending on who you talk to; the most common is the Revival of The Flash by DC Comics in 1956, but some say it happened before that, with the introduction of the Martian Manhunter in 1954, though many agree that it didn't kick into high gear until the appearance of Marvel's Fantastic Four in 1961.
It is also sometimes referred to as the Atomic Age (because of the nuclear paranoia in the 1950s affecting comics). Opinions differ on whether it should be considered part of the Golden Age or whether it counts as a separate age.
The Interregnum is often a case of Briefer Than They Think. It can be argued to be only five years (from the last appearance of the Golden Age Flash in All-Star Comics to the first appearance of the Silver Age Flash in Showcase), and even cherry-picking dates far apart is unlikely to make it more than ten years.
Notable series of the Interregnum:
- Adventure Comics: A long running DC Anthology Comic starring Superboy and also home to Golden Age survivors Aquaman, Green Arrow, and Johnny Quick.
- Captain Flash: One of the few superhero holdouts of the era. Both featured the titular character and Tomboy, one of the first kid superheroes to get her own strip.
- Detective Comics: DC's namesake title kept running through the 1950s, not only continuing the adventures of Batman but also introducing Martian Manhunter in 1955 (in his own backup feature) and Batwoman in 1956.
- Rawhide Kid: Western title from Atlas Comics (previously Timely, later Marvel), later taken over by Stan Lee and Jack Kirby.
- Strange Tales: A sci-fi/fantasy Anthology Comic from Atlas that served as a springboard for budding Marvel greats Stan Lee, Jack Kirby, Steve Ditko, Don Heck, Dick Ayers, and others.
- Superboy: Besides appearing in Adventure, Superboy was popular enough to hold down his own series.
- Western Crime Busters: A Western comic from Trojan Publications, featuring such heroes as K-Bar Kate.
- Yellow Claw: Another Atlas publication, this one only ran for four issues in 1956. The title starred Jimmy Woo, one of the first Asian American comic heroes, fighting against the titular Fu Manchu knockoff, the Yellow Claw. Notable for the first issue by Joe Maneely, who died unexpectedly young (and according to his Atlas contemporaries would probably have been a major force at Marvel Comics had he lived), and the latter three both written and drawn by Jack Kirby.