This includes fantasy and sci-fi.
My choice is the Combine.
A multi-universal species from half-life so absolutely immense and powerful that they reverse-engineered earth's technology, upgraded far beyond human ability, brainwashed some humans and had them invade themselves. They did this and stomped all resistance within 7 hours. This was done by a backwater lesser combine city mind you.
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Edited by Tartan 118: 5/26/2015 8:51:37 PMA lot of people are saying all-powerful reality-controllers win this contest. And that's all well and good until you realise anyone can invent such a faction and install them at the head of their respective reality. And then we have factions poking into other realities. Such as the Combine. Even more powerful. But is there a fictional faction/entity so powerful that it can pervade multiple fictions of [i]different[/i] authors and creators, so powerful that its influence spreads beyond the control of its own creator? More worryingly, a fictional being so powerful, it has enormous control of our very own reality. Ladies and gentlemen, may I present you the god of Abraham. Edit: oh, race. Erm. I guess the most influential real-world religion with a pantheon.