Curt Connors was an army surgeon who dedicatedly helped soldiers in war, but who lost his arm to an explosion. Returning after the war, he began experimenting with reptiles, trying to discover the secret to how they managed to regrow their limbs. After years of research, he believed that he had isolated the chemical compound that gave them this ability, and after successfully doing animal testing, tried the formula on himself. While it did indeed regrow his missing arm, there was an unfortunate side-effect. The formula also turned him into a giant lizard with super strength, speed, and even some wall-crawling abilities. It also gave him a new imperative to cleanse the world of mammals so reptiles would rule the Earth again. Thankfully, Peter Parker managed to synthesize an antidote to the serum that allowed Connors to become human again, but it proved only temporary, as Connors continued to struggle with his lizard side which would occasionally come out under stress or certain circumstances.