In 1971, Savage Tales #1 by Marvel Comics introduced the Man-Thing. Dr Ted Sallis who becomes fused with the Swamplands surrounding his laboratory through experiments, accidentily of course. Since Savage Tales was canceled immediately after its first issue, it would be a year and a half later that a second tale of Man-Thing would appear in Atonishing Tales #12, written by Len Wein. It was also Wein who penned the origin for the creature Swamp-Thing for DC Comics. The two characters are practically identical.
Marvel’s version of the swamp creature is a large, slow, human like creature living in the Florida Eveglades near the Seminole reservation. His human counterpart, Ted Sallis, was working on re-producing the super soldier serum that created Captain America. He is also tied to having done work with Dr. Curt Conners aka The Lizard of Spider-man fame.
Marvel used Man-Thing as more than an enviromental statement, actually tying into the actual Marvel overall Universe with guest appearances by Dr. Strange, Howard the Duck and Spider-Man. In transforming into the Man-Thing, the intelligence and memories of Dr. Sallis are lost so all that remains is the Man-Thing, a plant like humanoid that reacts on instinct and not on thought.
In our current enviromental and cultural climate, it is surprising that Marvel has not tried to do more with Man-Thing. Maybe its because he is called Man-Thing and that is too gender specific for Marvel?