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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I would say the Jew. They are not a race, but Semites, members of a linguistic group. The same group as Arabs. So Jews and Arabs are the same race. And I say they are powerful because they made their own country, Israel, by committing genocide on the indigenous peoples of Palestine. They continue to do so today, and their powerful zionist lobby has all the governments of Christian nations by the *blam*.