Cosmic Boy is from DC Comics Legion of Super-Heroes, which is the 30th(?)-century version of The Justice League. They are also famous for having some of the most ridiculous superhero names.
The Legion of Super-Heroes have such members as Matter-Eater Lad, Karate Kid, Invisible Kid, Lightning Lad.
Maybe I'll start uploading a quickpaint of every member of the Legion...
Here's a list of all the members of the Legion: https://en.wikipedia.org/wiki/List_of_Legion_of_Super-Heroes_members#Founding_members
Drawn in Clip Studio Paint Pro on a Surface Pro 4. Here is the timelapse video: