Since the beginning of the comic book industry, accusations of plagiarism, stolen ideas, and blatant rip-offs have been common. One of the oldest such cases, that between Marvel's Man-Thing and DC's Swamp Thing, is actually an instance of both publishers copying the same Golden Age character. Marvel and DC have been in fierce competition with one another since the 1940s, but their rivalry truly heated up in the Silver Age.
Source：https://www.cbr.com/man-thing-swamp-thing-true-inspiration/
