Dr. Curt Connors was a brilliant scientist who lost his arm during military service. In an attempt to regenerate it, he developed a serum derived from reptilian DNA, which transformed him into the Lizard. This transformation grants him superhuman strength and agility but also leads to a loss of his human intellect, making him a tragic figure in Spider-Man's rogues' gallery. His battles with Spider-Man often explore themes of duality and the struggle between his human side and the monstrous Lizard.