"The seed is strong."
―Jon Arryn before his death.

Lord Jon Arryn was the head of House Arryn, Lord of the Eyrie, Warden of the East, Lord Paramount of the Vale, Defender of the Vale, Keeper of the Gates and the Moon and, late in his life, the Hand of the King. Ned Stark and Robert Baratheon were his wards as children, where he became a sort of father figure to them, as well as their mentor. He fought in Robert's Rebellion after one of his nephews was executed by Aerys II Targaryen. When Robert became the new king, Jon Arryn became his Hand. Seventeen years after Robert's rebellion, Jon Arryn suddenly and abruptly fell ill and died: it was later revealed he had been poisoned as part of a plot by Cersei Lannister to keep the true father of Robert's children a secret. In reality, she was framed, as Lysa Arryn had secretly done so at the behest of Petyr Baelish.