The Kings of the Iron Islands
A people who decided that taking things was a religion, and have been losing wars about it ever since.
The fuller tale
The ironborn trace themselves to the Grey King, who is said to have ruled a thousand years, married a mermaid and made a hall of the bones of a sea dragon; the Citadel's view of this account is not recorded, but can be guessed. What is real is the Drowned God, the iron price, and the salt kings and rock kings who once chose their high king at a kingsmoot on Old Wyk.
At their height they held the whole western coast and the riverlands with it, and the Hoares ruled from Harrenhal. That ended in one afternoon when Balerion came over the walls. Aegon then let the islands choose their own lord, and they chose House Greyjoy, who had been kings before and have never entirely stopped acting like it.
Twice in living memory a Greyjoy has crowned himself, and twice the arithmetic has been the same: a few hundred longships against a continent. The islands are stony, poor and thinly peopled, and the whole culture is an argument that this is a virtue.
The ground they held
 See the world in 3 BC on the timeline What became of it  if an ending is written, it is here. Spoilers.
The chronicle records no ending here ÔÇö or none the maesters have set down.