Where a god can breathe a soul into a body, mortals, no matter how gifted, lack that skill. But some very rare men over the course of history duplicated the story of myth, by bringing life to a dead body. Life, fueled by Pyros, but without a soul, without humanity. Those men are now long dead, the ones who are known to have mastered this art. But their creations live on. And reproduce.
Promethean is a game set in the World of Darkness, a contemporary world like ours but with deeper shadows, where the worst sort of urban legends, occult mysteries and conspiracy theories are usually true. As such, contemporary issues such as science are not treated as science fiction, with technologies like robots and spaceships that don't exist yet, or mad scientists creating false life in sterile laboratories. Instead, these issues are seen in the half-light of ancient mysticism and magic. The force that animates Prometheans is not made of nanotech; it's a mysterious energy spoken of in ancient myth: the Divine Fire of the gods. The beings who make monsters aren't scientists trying to prove their crackpot theories - they're other monsters seeking to assuage their loneliness or to hand off their curse so they can escape it themselves.
In short, Promethean is a modern horror game, tinged with elements from medieval alchemy, ancient myth, and modern occultism. It's a game about monsters who want to be human. Despite their strength, endurance, and amazing powers, they envy mortals, for as weak, petty and ignorant as we mortals can be, we have something Prometheans don't: We have each other.