>>214001090
Originally, Swamp Thing generally fought classic horror movie monsters. Werewolves, vampires, etc. His gimmick was that he was a man who'd become a monster in a horrible lab accident and, as he traveled the world searching for a cure, he encountered other traditional "monsters" and generally the twist at the end would be that they were all just as misunderstood and feared as he was.
Then for a long time he just fought whoever. He sort of got shuffled into the "standard" DC roster and did some globe-trotting supervillain fighting.
Then Alan Moore got ahold of him and rebooted everything about him, effectively creating the modern Swamp Thing. DC now has the concept of elemental planes, such as "The Green" (plants) and "The Red" (animals). Swamp Thing is the guardian elemental of The Green, and he spends a lot of his time fighting rival elementals as they plot to undo the balance of the world. He also has a ridiculous power level at this point, so people often want a piece of him, and he spends a fair amount of time battling nefarious scientists or organizations that want to harness his power. He also cameos as a sort beholden-to-nobody third party with Justice League stuff occasionally, since almost everything they do affects him in one way or another. Beyond that he just sort of has the bog standard "protect the environment" villains of evil corporations dumping toxic waste or whatever.
