The rejects are a group of exactly what the name suggests, superheroes who were rejected from al the other teams.
The group was sarted by the alien Darkmind after beig rejected from the justice league because he was a Xenomorph, albeit a Martian Xenomrph. AFter this he decided to make up his own group for other superheroes wo were rejected or kicked out of all the ther superhero groups and organizations for unjust reasons. After setting up their HQ built on top of a Mesa they set out to become well known. Unfortunatley they are still relativley obscure, and for this reason most suerhero groups don't trust them and villians dont know them. However this does not stop them from trying to be recognised.