Second daughter of Lord Hoster Tully of Riverrun and younger sister to Catelyn Stark, wed at her father's command to Jon Arryn in the same week her sister wed Lord Eddard, sealing the Lord of the Eyrie to the cause of the rebellion. Before the wedding she had loved her father's ward Petyr Baelish and lain with him in his cups, and her father had purged the child from her womb with moon tea, a wound she carried into her marriage and could not be persuaded to set aside. Of the many children she lost or saw stillborn in the years that followed, only one survived to weaning: a small, sickly boy she named Robert.
After Lord Arryn died at King's Landing in 298 AC she fled the capital with her son and shut the Bloody Gate behind her, refusing all summons from king and council alike. She sent a letter in secret to her sister at Winterfell laying her husband's death at the Lannisters' door, took the prisoner Tyrion Lannister at the high road and made a mummer's farce of his trial at the Eyrie, and ruled the Vale as regent for her son until Petyr Baelish came at last to claim her hand. He pushed her through the Moon Door at the High Hall not a fortnight after their wedding, and the Vale answered to the Lord Protector thereafter.