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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The only correct answer: [spoiler]Cybertronians, from the Transformers franchise. They are technologically advanced to levels BEYOND understanding. They have incredible abilities and weapons. And the ability to turn into any vehicle you find and disguise yourself, absolutely AWESOME!!!!![/spoiler]