The Origin Of The Justice League -- Minus One
After destroying a cache of Martian weapons found on Earth (in Detective Comics #264 in February, 1959), J'onn was confronted by Commander Blanx, the white Martian who had sent J'onn into exile.
Mirror Master (in Flash #105 from February-March, 1959). J'onn and the other Martians escaped the Flash when confronted by paranoia from the residents of Middleton, who felt they were being invaded.
They were even suspicious of new hero, Flash, so he went to Metropolis to attract the attention of someone everyone would trust....Superman. Superman did indeed show up (from Action Comics #249 of February, 1959), with Batman and Robin in tow (these three already a team), but, they also attracted the attention of Roy Raymond, TV Detective, who advertised for more heroes to come....and boy did they! All the heroes (plus Daily Planet reporters Lois Lane and Jimmy Olsen) split up to cover three different reports of alien invaders.
Team OneThe first team was composed of:
The heroes faced off against a mysterious man in a cabin, who disappeared from that house, even though it was surrounded by the heroes.....and where (and when) he went to was revealed as he first appeared a little later, in Showcase #20 (May-June, 1959), and you can figure out who he is by going here!
Team TwoThe second team was made up of:
Congo Bill first appeared in More Fun Comics #56 (June, 1940) as a big game hunter, but added a magic ring that allowed him to exchange minds with the golden gorilla, Congorilla, in Action Comics #248 (January, 1959), and the two last appeared in Action Comics #249 (February, 1959).
Robotman is even more confusing, having started out on Earth-2 in Star-Spangled Comics #7 (April, 1942), having his human brain transferred out of his dying body into the robot form, later retroactively appearing in World War II group All-Star Squadron as a member, he must have left Earth-2 for Earth-1 sometime after Detective Comics #202 (December, 1953), his last Golden Age appearance.
This batch faced a flying menace in the woods, who was chased by all the heroes, except Lois, who figured out the mysterious figure was trying to get them to leave and area, but, that spaceman did disappear after being hit by an energy beam (and he explained it to his girlfriend, as these two were appearing between Showcase #18 and #19 of 1959; he later helped Superman save Lois and Earth, as explained here).
Team Threecharter members of the Justice League of America:
Superman, Batman, Wonder Woman (coming from Wonder Woman #104 of February, 1959), Aquaman (last in Adventure Comics #256 of January, 1959), and the Flash!
These heroes ended up out on the west coast, in Coast City.
Batman's partner, Robin (who first appeared as an Earth-1 version in Superman #76 from May-June, 1952, and was last in Detective Comics #264 from February, 1959 with Batman).
Roy Raymond, TV Detective, who was the host of the Impossible But True TV show, and premiered in Detective Comics #153 (November, 1949), but appeared here along with his assistant, Karen Duncan, fresh from Detective Comics #264 (February, 1959) and getting the scoop for his viewers.
Green Lantern, who, unbeknownst to the heroes at the time, was test pilot Hal Jordan!).
joined the JLA later), as he and his ward, Speedy, had just solved a case on the island that created the Green Arrow (as revealed in Adventure Comics #256 of January, 1959) and had stayed for a little vacation, missing out on the invasions)...
they formed again facing the Appellaxians), and the recent brief return to Earth for a bit of the Martian Manhunter.