Alec Holland was a famed botanist working on a chemical to increase plant growth and durability, but a rival chemical company sent mobsters to force him to stop his research in his remote, swamp research cabin. When Holland refused, the mobsters planted dynamite in his laboratory. The resulting explosion killed Holland's wife instantly, though Holland was soaked in his experimental chemical and hurtled, burning, into the swamp. Days later, he arose, no longer Alec Holland, but now the Swamp Thing, a plant being, and avatar of nature itself.
- During the springtime seasonal event, the hero must fight Swamp Thing in Sewer Rendezvous to cure him from Poison Ivy's poison.
- During the springtime seasonal event, Villains need to fight him in Sewer Rendezvous to save Poison Ivy's plan from ruin.
- The Swamp Thing is the last boss for Villains in the Tier 4 Seeds of Rot Operation from the Hand of Fate DLC.
- The Swamp Thing first appeared in House of Secrets #92 (July 1971)
- The Swamp Thing's voice is provided by voice actor Chilimbwe Washington.