Membership: Stone-God, Glass-Man, Mercury Monster, Golden Roc, Fire-Lord, Crystal Creature, and Wood-King
First appearance: Justice League of America I#9 (Feb. 1962)
Abilities: Various
Worst act: Transforming people into stuff
Quote: "So your weakness is fire, Man of Mars? Then that's how I shall overcome you!"
Created by: Gardner F. Fox (script), Mike Sekowsky (pencils), Bernard Sachs (inks)
Technically this could have been published on the 1st, given this is the first proper origin story of the Justice League, but we'll have it here for completion's sake.
The aliens here are all competing for the throne of their home world Appellax. They just decided to compete on Earth and change as many people as they can.
Landing across the globe, each alien attacks the local pop but thankfully a future League member is nearby to stop them. A slight breakdown:
Stone-God (Martian Manhunter)
Glass-Man (Aquaman)
Mercury Monster (Wonder Woman)
Golden Roc (Green Lantern)
Fire-Lord (Flash)
Getting together to see how many meteors crashed to Earth, they discover they all missed one. Rushing to the next one to tackle it, they find themselves turning into trees but thankfully they work together and stop the Wood-King. They next head to Greenland to face the Crystal Creature, but there they find Superman and Batman having already cracked the case.