Merryk Greyjoy was the eldest son of Damron Greyjoy and Alannys Greyjoy. He was killed by a boy of House Manderly while raiding Greywater Watch.
During the Second Greyjoy Rebellion Merryk took his men inland, despite his father's wishes, and was killed while raiding Greywater Watch, leaving his younger brother, Aeron Greyjoy, as heir to Pyke.
"Dagon and Aeron were two halves of their older brother, who had been gentle and merciless in equal parts, with the intelligence to know which side to show when." - Blood and Whispers
Damron Greyjoy, father (deceased)
Alannys Greyjoy, mother
Gwynesse Lannister, aunt (deceased)
Aeron Greyjoy, brother
Dagon Greyjoy, brother
Gwin Greyjoy, sister