During the wars fought between the King of the Iron Islands and the King of the Rock, Herrock the Whoreson used his horn to signal for the whores of Kayce to open the postern gates. His men then captured the town for House Lannister. Three different Ironborn kings tried to retake the town, but were defeated. Herrock personally killed two of them.
Herrock's horn is still passed down by his descendants.