All-Star Squadron was created by Roy Thomas with Rich Buckler and first appeared as a preview story in Justice League of America (DC, 1960 series) #193 [Direct] (August 1981).
The premise of the team was that after American entry into the Second World War (WWII), all the mystery-men (superheroes) of Earth-Two were placed into a single team under the direction of U.S. President Franklin D. Roosevelt for the duration of the war.
The team was meant to consist of all the WWII era heroes from the DC Universe (originally in the 1940s under Detective Comics and All-American Comics companies and those created later on for that time period by National Periodicals and DC Comics). Thomas also incorporated the heroes that appeared in Quality Comics during this time (DC purchased Quality in the mid-1950s).
Eventually, characters from Fawcett Publishing crossed over (DC leased then later purchased their rights by the early 1980s), and after the Crisis on Infinite Earths storyline which wiped several heroes from that era from the comic's continuity, new characters would be created (Young All-Stars) and heroes of that era originally from the Charlton Comics Universe were scheduled to join as well (DC purchased Charlton heroes in the early 1980s).