The Lizard
The Lizard is the alternate form of Dr. Curt Connors and an enemy of Spider-Man. The Lizard was born when Dr. Connors developed a serum to re grow his missing arm. At first it appeared to be fine but he soon mutated into the Lizard. He was eventually cured thanks to the combined efforts of Spider-Man, Eddie Brock, Martha Connors, and Gwen Stacy.
In Ultima, although Connors was cured of his transformation, Padro Lodo did not want to see such a powerful beast go to waste. So, he had Master Xehanort go undercover as an old pedestrian and trick Dr. Connors into coming close enough to him so that the old keyblade master could stab the good doctor with his keyblade and extract the darkness within his heart. This darkness was cultivated and transformed into an all new Unversed version of the Lizard that was raging mad and angry and had no intelligence whatsoever. But Master Xehanort fixed that problem by implanting a shard of his own heart inside the Lizard's being, giving it the same malevolent cunning and intelligence as Xehanort. As a result, the Unversed Lizard was recruited by Padro Lodo into the Organization as a member of the Neo Masters of Evil.
The raeson why the Lizard wanted to rule the world and turn everyone into reptiles is because that isn't Connor's mind who planned this, it was actually the Xehanort heart shard that twisted and corrupted the Lizard's mind, making it believe that mammals had outlived their capacity to evolve further and that reptiles need to regain their evolutionary spotlight for the sake of the planet's ecology. Besides, the heart shard made the Lizard believe that since he was the first of the new race of Reptilihumanoids, he should be the one to lead them to a great and powerful civilization of the future. Not only that, but the heart shard made the Lizard believe that no one would accept him into their society and that they need to be shown the error of their ways and become companions to the Lizard so that he wouldn't be alone in his suffering. This Unversed Lizard first appeared in Spiderman VS the Joker, where he, along with many other supervillains, was ordered by Padro Lodo and Maleficent to invade Gotham and New York, ransacking it for the Organization's plans.