David Michael Gray first appeared in X-Men #30.
From what's been shown, he was a common gen-biologist. His origin isn't known or anything which goes further then that. He recently came back into the open due to his ignoble dealings with mutants which date back to the Black Plague era.
Full of curiosity, Gray decided to experiment with a branch of the mutant race which were faced with genocide many decades ago. With the DNA that had been found, he began producing what are called "Proto-Mutants" and planting them in heavily populated district centres, allowing the distorted things to wreak havoc and destruction in the areas that they were placed in. Utopia's Security Team were made aware of this when they encountered one of his monsters in Grozny, further information was obtained when their accomplice, the Mutantes Sans Frontiers, deciphered a top-secret sample given to them, in doing so, Gray continued his evil doings. Another of his monsters had been let loose in Quebec, by David, but unlike the others, it did not die upon contact, the Security Team took him in, but, unbeknownst to them, Gray was still experimenting with some others, he also had tabs on that particular monster who went by the name of "Ister", Gray saw the monster as collateral damage and in an act of spite and complaceny, terminated Ister while he was in the care of the Security Team, luckily, while Ister was dying, the resident telepath of Utopia's Security Team, Betsy Braddock, managed to grab a hold of his conciousness and his memories, the location of Gray was now known.
The Security Team prepared themself to face off against him, he was aware of their coming and awaited it, Colossus of the Security Team apprehended him in rage, Gray didn't want to give away too much but made it clear that this would not be the last of the Proto-Mutants, quickly, Gray shot himself in the head at point-blank range.