This is a horror comic book from DC Comics created originally by Len Wein and Bernie Wrightson. The main character Alec Holland, a scientist working on a bio-restorative formula, who was caught in a fire from a sabotage attempt in the Louisiana Bayou. His burning body falls in the swamp and he later emerges as a creature of plants.

The initial run was short lived and then when it was revived it still did not seem to catch the public imagination until a young british writer called Alan Moore took it over. His second issue (#21) "The Anatomy Lesson" turned the entire series on its head. With the original writer Len Wein editing the book he proceeded to totally change both the premise of the book and its atmosphere to create a phenomena.

Rather than a man who had been transformed into a plant (and could hope to be restored to humanity) the Swamp Thing was revealed as a plant that thought it was a man. In later issues it becomes even more complex and it is revealed that he is not the first Swamp Thing and that the Swamp Things are earth elementals.

The stories became very dark and strange. There is an entire sequence called "American Gothic" that is full of very eerie and unsettling stories (including one about the house built by I think Colt where the sound of the carpenter's hammer should never stop). It was part way through this sequence that the Comics Code Authority actually read an issue (after spying a particuarly graphic page) and demanded in effect a total rewrite. DC in reponse instead removed the CCA stamp from the cover and stopped even submitting issues for certification.

There were also a series of B-movies based on the comic book. However my limited experience of them suggests that the less said the better (maybe someone else with more knowledge of them can add a node)