Gerold Lannister

"When the ironborn became a nuisance, my ancestor sailed to the Iron Islands and returned with a hundred ironborn hostages, promising to hang one from the rock every time the ironborn dared raid our shores. The ironborn stayed away, well, after twenty or so."

- Jaime Lannister

King Gerold Lannister was the King of the Rock.

King Gerold sailed to the Iron Islands when the ironborn began causing him trouble and captured a hundred of them. He promised to hang one from Casterly Rock every time the ironborn raided the shores of the Westerlands, and they eventually stopped their invasion after twenty of them had been hanged.

In the books
In the A Song of Ice and Fire novels, his story is the same.