Chameleon is possibly a part of the Saurian race, of which Reptile and Khameleon are members. This has never been conclusively stated in any of the games and is purely speculation on the part of the fans at this point due to his reptilian name, green blood, and the reptilian titles of his special moves in Armageddon. He has even shared similar features with Khameleon in both of their appearances, furthering the speculation.
If he is a Saurian, that would mean that Reptile is not the last living male of his species, which had been previously stated in Khameleon's biography screen. However, the release of Armageddon did not address this issue.
In Mortal Kombat: Armageddon, he is finally given a rather vague backstory, stating that he had been present at events dating all the way back to Liu Kang's victory in the first Mortal Kombat tournament, constantly remaining hidden in the shadows and biding his time while watching the events unfold.
- Armageddon: "As the battle raged, Chameleon camouflaged himself and raced to the top of the pyramid unseen. There he defeated Blaze and the ethereal power overtook him. Immortality was now his! Though he had been ever-present throughout the crises of the realms, from Liu Kang's first victory to the return of the Dragon King, he had remained hidden from sight, waiting for his moment to come. That moment had arrived. From this day forth, the realms will know Chameleon as the true champion of Mortal Kombat!"