Dr. Curt Connors was a biology teacher at ESU and scientist studying reptiles and cell regeneration. After losing his arm in an explosion, Dr. Connors devoted his life to creating a serum which would regenerate lost limbs. Using DNA from reptiles, who naturally regrew limbs, Connors created a serum he was sure would work. He injected himself with a dose of the formula, and was ecstatic when his arm began to regenerate.

However, shortly afterwards, he mutated into a vicious reptilian creature known as The Lizard. The Lizard battled Spider-Man, who was eventually able to “cure” him and turned him back into his human form. Dr. Connors soon discovered that in times of anger, stress or sadness, his body would revert back into his reptilian form.