Created by Lein Wein and Bernie Wrightson, big vegetable guy Swamp Thing first appeared in House of Secrets #92 in the 70s with the name Alex Olsen. set in the early 20th century, when scientist Alex Olsen is caught in a lab explosion caused by a co-worker, who wanted to kill him for the love of his wife. the explosion from the chemicals physically altered Olsen into the Swamp Thing.
After the success of the short story, Swamp Thing #1 debuted by Wein and Wrightson now based in the mid 1970's and featured a new character named Alec Holland as the monster. The origin is almost the same except that this time the explosion was due to sabotage. Now Swamp Thing is pretty much a rip off of marvel's Man-Thing (I know its a funny name) that was created years before Swamp Thing. They look pretty much the same with similar backgrounds. Even, Wain worked on Man Thing before Swamp Thing; is amazing that marvel never sued. Thank God for that!
Alan Moore, took over and Swamp Thing was reinvented into a elemental deity. You see, Alec Holland was always dead instead the monster absorbed Holland's memory and personality. In a way the monster thought it was human. This really made Swamp Thing into a very distinct character from that other Marvel Character with the funny name. Also Alan Moore's run on the character is consider to be a groundbreaking point in comic book history. For introducing mature content and experimenting with story telling. The book won Jack Kirby awards among many others. Also Swamp Thing is one of the rare characters that has bested Batman.
Although Moore is not the only big time writer to grace this book, writers like Mark Millar, Grant Morrison, Brian K Vaughan and many others had written runs for this character. Also there has been countless Swamp Things all over history but none like Holland. In the 90s Holland's daughter Tefe took over as the main Swamp Thing and later another man took over the reigns but after that the series got canceled. Swamp Thing has superhuman strength and can control any form of plant life. He can make it move to his will or manipulate its growth plus swamp thing doesn't need a body as he can re-grow in any plant. At one point Swamp Thing was a major character almost rivaling Batman and Superman in popularity, if you don't believe me just look at what this character has done.
This character is consider to have stablished the first Vertigo line of books. It also was the first book to featured John Contastine. Swamp Thing is one of the few obscure characters that has two movies, a TV series and an animated series. Sadly Swamp Thing stopped being cool in the 90's due to wandering plot lines and low sales. But if you want to check this character out, check the trades from the 70's and 80's. Alan Moore's run is collected in four hardcovers and is now in digital form on the DC Comixology app.