Basic Trope: Before mankind came to dominance, the world was ruled by evils beyond imagination.
Straight: In Heroes of Troperia, a species of Eldritch Abomination known as the Chthonian ruled the planet. They were utterly amoral and everything was just a plaything to them. But the slaves —humans, elves, catfolk, and whatnot— rose against them in planet-wide rebellion, and the Chthonian overthrown; now they slumber Beneath the Earth.
The Chthonian ruled the galaxy.
The Chthonian ruled the entire universe.
The Chthonian are the universe. Let that sink into your mind for awhile...
Downplayed: The Chthonian were terrifyingly powerful beyond human comprehension; but by human's standard, they were no more Good or Evil than humankind.
Inverted: The world of Heroes of Troperia used to be a paradise designed and ruled by the Chthonian. But their servants —humans, elves, catfolk, and whatnot— overthrew them out of plain old Envy. Ever since then, it's a Crapsack World.
Subverted: The now-extinct Chthonian built terrible devices that no sane person today will even think of making, but they did so out of the planet's best interest: to fight the truly terrible Eldritch Abominations roaming the void between stars.
Parodied: The Chthonian were a race of Magical Girls who shape the world according to their Rule of Cool and Rule of Cute, forcing everyone to play along with them. Didn't make them any less terrifying, but if the world has always been a stage, the play back then was Black Comedy.note Sounds kinda like Exalted, doesn't it?
Zig Zagged: The Demons said that the terrible Chthonian —who created them— used to rule the world, but Demons are Consummate Liars. But then, you just have to wonder just what kind of people brought something as awful as Demons into reality...
Discussed: Two wizards with archaeological bent discuss about what would happen when the ancient civilization whose books they are studying were vastly more powerful and vastly less moral. They believe that it would have been this trope.
After all the crap the Chthonian put the world and its inhabitants through, the world is an utterly broken place— even after the Chthonian were long gone. In fact, the races that overthrew them start behaving like the Chthonian because they don't know other ways of dealing with the situation.