It is common knowledge in comic book circles that Marvel and DC have, over the many years that both giants of the industry have been in existence, ripped each other off. Every Marvel hero (and, in many instances, villain) seems to have either a pre-existing or post-dated DC equivalent - Ant-Man and Atom, Deadpool and Deathstroke, Hawkeye and Green Arrow, the list goes on and on and on.
The myriad similarities in both company's rosters is a product of their close and often intimate relationship over the years. Both companies were founded (and are still based in) New York City, as were a number of other smaller publishers that have gradually been absorbed by one or the other. NYC being the epicenter of the comic book universe meant that every artist and writer worth his salt was based there, and a great number went between Marvel and DC over the years.
This back-and-forth of a number of influential comic book creators over the years cultivated an environment that was accepting of, and almost encouraged copying from the rival to the near-point of plagiarism. Yet, while the practice of ripping-off superheroes from each other became common, less common was the blatant and direct copying of an entire story arc.
Thanks to the MCU, one story that everybody seems to be familiar with now is Marvel's Civil War, though fewer people are familiar with the DC story that it blatantly copied. Mind you, DC (while perhaps the less guilty of the two) aren't entirely innocent either, as you're about to see for yourself. It seems all is fair in love, war and comic books.