You wouldn't think the concept of a sentient conglomeration of plant matter and mud would be the sort of thing that creator after creator would rush to duplicate (i.e., rip-off). And yet, you can probably think of Swamp-Thing or, if you're a Marvel fan, Man-Thing right off the top of your head, and you're well aware of the other company's similar swamp monster.

While it's often been debated whether Swamp Thing or Man-Thing was created first, the truth is both of them had a number of predecessors that came oozing out of their respective swamps first, as far back as 1942. There are plenty of true swamp beasts to go around, as it turns out. Here are 10 of nerd-dom's most famous.

10) It!
The grandaddy of them all, 1940's "It" is the name of a short story by American science fiction and horror author Theodore Sturgeon. Published in Unknown in August 1940, "It!" tells the story of a man who dies in a swamp. Over the years, the plant life forms around his skeleton to create a shambling, barely-sentient monster. Sound familiar? If not, it will by the end of this list. All swamp monsters basically owe their existence to this story. The story was adapted for the first issue of Marvel's anthology horror series Supernatural Thrillers in 1972 by Roy Thomas, Marie Severin and Frank Giacoia.

9) Bog Swamp Demon
The Bog Swamp Demon first appeared as a back-up story in the Mirage Teenage Mutant Ninja Turtles series (specifically volume two, issue six, in 1994). A few years later, Bog got his own miniseries with covers by famed Swamp Thing artist Stephen R. Bissette. Bog's character was something of a cross between Swamp Thing and DC's Etrigan, in that he was a swamp-based demon. His look was essentially a demonized version of Swamp Thing (or Man-Thing, etc.) The story itself was sort of like Swamp Thing meets Spawn, with Bog fighting various demonic threats while occasionally fighting off threats against himself from Heaven.

8) The Glob
Issue #121 of The Incredible Hulk (1969) told the story of Joe Timms, an escaped convict who drowned in a swamp (polluted with radioactive waste for good measure). He was transformed into a pile of semi-sentient swamp muck known as the Glob, who fought the Hulk a few times before being eventually transformed into a clay-based creature. Most recently he was recruited into S.H.I.E.L.D.'s Paranormal Containment Unit. While his origin is obviously reminiscent of Theodore Sturgeon's "It" or Solomon Grundy (see below), in many ways the Glob seems to more closely resemble the second Clayface, Matt Hagen, who was introduced in Detective Comics eight years before the Glob's debut. There was also a second, much shorter-lived Glob in the Marvel Universe, too.

7) Force of Nature
Like Dungeons & Dragons before it, the early editions of Magic: The Gathering borrowed from every aspect of fantasy, science fiction and horror literature in developing its cards. In the early days every color had its own badass creature: red had the Shivan Dragon, black had the Lord of the Pit, blue had the Mahamoti Djinn, white had...well, white didn't have anything really (until the Serra Avatar showed up years later), and in 1993, green had the Force of Nature. The Force of Nature was expensive to cast, and if you didn't feed it green mana constantly it would turn around and punch you in the throat (metaphorically speaking), but its "trample" ability meant whatever piddly creature your opponent threw in front of it would barely slow it down.

The original edition of Force of Nature had no "flavor text" describing the character, but the art on the card was a very obvious reference to any number of creatures on this list (but most likely Swamp Thing). Later art depicted it as less of a Swamp Thing rip-off and more of a Treebeard-rip off.

6) The Shambling Mound
First appearing in the official TSR newsletter in 1975, the Shambling Mound later appeared in the very first Monster Manual in 1977. While resembling heaps of rotting vegetation, Shambling Mounds are actually carnivorous plants. Clearly inspired by the Heap, Swamp Thing and their ilk, the Shambling Mound continues to menace dungeon crawlers to this day.

5) Moss Man
Mattel's mid-1980s Masters of the Universe line was very similar to Dungeons & Dragons in that it borrowed from everything fantasy, science fiction and horror had to offer. So perhaps it's no surprise that MOTU got its own swamp monster in the form of Moss Man, a nature-loving hero whose action figure was famously covered with a Chia Pet-like coat of green flocking.

In the 1980s cartoon, Moss Man was little more than a spy who could talk to plants and hide himself among them. But for the 2003 cartoon he was given a Swamp Thing-like makeover into a vegetative god with immense powers over nature and plant life. He was so powerful, he could only make rare appearances on the show, because otherwise he'd just defeat the bad guys instantly and there would be little dramatic tension.