After being among the original six Avengers, Marvel's Hawkeye has his show now. However, it is similar to DC's archer, Green Arrow, who also uses gadgets with his arrows. Notably, DC introduced Green Arrow twenty years before Marvel brought in Hawkeye.
DC introduced Batman's nemesis, Catwoman, in 1940. She wears a tight black leather suit. Later in 1979, Marvel introduced Black Cat, a similar-looking character who has a dalliance with Spider-Man.
Thanos was one of the biggest and strongest supervillains in Marvel's Avengers. However, he's not an original. He looks like one of the rip-offs of Darkseid, a New God in DC.
Marvel did not introduce the idea of a superhero shrinking in size with Ant-Man. It was DC who did it in 1961 with The Atom. It mimicked the pattern of a white dwarf star to reduce its density and shrink in size.
Gladiator was a homage to DC's Superman. Gladiator's real name, Kallark, was a mix of Superman's Kryptonian and human names, Kal-El and Clark Kent.
DC launched Red Tornado in 1968. Two months later, Marvel launched Vision. The red-skinned androids had striking similarities in their characters, especially their costumes.
It might shock people when they discover that their favourite Deadpool is not an original. Marvel based it on Deathstroke, a villain who appeared in DC's New Teen Titans.
X-Men and Doom Patrol are not similar but identical concepts. They have superhuman misfits led by wheel-chaired masterminds who protect the world. However, Doom Patrol hit the newsstands three months before the first edition of X-Men.
Like Green Lantern, Nova receives his powers from a dying alien. Later, he joined Nova Corps, intergalactic police, like Green Lantern, who joined Green Lantern Corps.