Is not this simpler? Is this not your natural state? It's the unspoken truth of humanity, that you crave subjugation. The bright lure of freedom diminishes your life's joy in a mad scramble for power, for identity. You were made to be ruled. In the end, you will always kneel.
Tyrants, or Evil Rulers, are powerful villains who seek to conquer, or have already conquered, a certain area. Their territory can range from a city, to a particular region/country, to the entire world, to an entire galaxy or galaxies, to even the entire universe or cosmos. They often seek complete domination of whatever territories lie out of their influence but not always, for some are content to rule small to mid-sized territories and do not seek expansion on larger scales (this differs them from Imperialists and Totalitarians, who seek to reshape not only their own society but often the world itself (in some cases they even seek to reshape the universe itself).).
Examples include Sauron in the Lord of the Rings franchise, Frieza in the Dragon Ball franchise, and Emperor Palpatine in the Star Wars franchise.
NOTE: NOT to be confused with Cosmic Entities who are practically gods and not simple dictators, and Hegemony who wishes to be a Tyrant, but failed/yet to be able to fulfilled their said goal.
Dictators in The Evil Wiki, for further information about Tyrants that happened to be dictators.
Dark Lords/Ladies in The Evil Wiki, for further information about Tyrants that happened to be dark lord/ladies.