Jon Arryn

Jon Arryn took two boys as wards and got a rebellion for his trouble. When the Mad King demanded the heads of Robert Baratheon and Eddard Stark, the old Lord of the Eyrie sent back defiance instead of obedience, and the Seven Kingdoms tipped into war. Everything that followed — the Trident, the sack, the throne — began with one man declining to hand over the children he had raised.

As Hand of the King he ran the realm for fourteen years while Robert hunted, drank, and complained about being king. It was steady, unglamorous, largely thankless work, and it held the peace together. He died suddenly, having started asking questions about the queen's golden-haired children, and every catastrophe that follows in this story unspools from the hole his death left behind.