Dalton Greyjoy
The Red Kraken: Lord Reaper of Pyke at sixteen, with a dozen salt wives and a longship's patience for other people's wars. Both crowns write to him; he answers the one that lets him reave.
The fuller tale
Called the Red Kraken, Dalton Greyjoy becomes Lord Reaper of Pyke at the remarkably young age of sixteen, and rules the Iron Islands thereafter with a dozen salt wives and a longship captain's patience for other people's continental squabbles — an ironborn lord who treats the Dance chiefly as an opportunity rather than a cause.
Both crowns write to him seeking the Iron Islands' fleets and support; Dalton, characteristically, answers whichever side's terms let him do the most reaving along the way, treating the entire war as a particularly generous excuse to do what ironborn lords do regardless of who currently sits the Iron Throne.
The page and the screen
Dalton Greyjoy appears only in Fire & Blood; the show's current seasons have not introduced the Iron Islands' role in the Dance at all, leaving this entire thread of the book's account of the war currently absent from the series.
Their fate — if death has found them, it is written here. Open at your peril.
The chronicle records no death for this soul — they are living when the tale leaves them, or their ending is a page the maesters have yet to turn.