MacDonald Gargan, also known as the Scorpion is a criminal with arachnid DNA matching Spider-Man's.
Mac Gargan got into an accident which caused him to gain a tail and arachnid DNA, making him the Scorpion. He then made his way to New York.
When Mendel Stromm found his DNA was matching Spider-Man's, he sent the HKs to capture him and Spider-Man, which forced them together in the sewers. They then battled the HKs, but Scorpion turned on him and attacked Spider-Man, though Spidey defeated him and he escaped.