The eldest son of House Greyjoy.After the Greyjoy family was defeated by the Stark family, they were taken away as hostages by the Stark family and raised as their own children by the Stark family.
He betrayed the Stark family at a critical moment and was tortured by the perverted son of Stark's lieutenant into a slave who obeyed unconditionally like a machine.
After seeing Sansa, he regained his sanity, protected Sansa from the crisis, and then defected to Daenerys.