Aerys II Targaryen

Aerys came to the throne in 262 AC at nineteen, and the early years of his reign are remembered, when they are remembered kindly at all, as a season of peace and plenty. The turn came gradually: repeated stillbirths and the deaths of infant sons wore at his queen and himself both, and his temper hardened into something crueler with each loss.

The Defiance of Duskendale in 277 AC broke whatever balance remained. Lord Denys Darklyn held the king captive for half a year before Ser Barristan Selmy freed him; Aerys emerged from that captivity gaunt, paranoid, and convinced — not without some cause, though he trusted no one enough to test the theory — that his own Hand, Tywin Lannister, had let him rot there on purpose. From then on he trusted fire and dragons' blood more than men, and set his pyromancers to hoarding wildfire under King's Landing against a day he alone could foresee.

When Lord Rickard Stark came to King's Landing in 282 AC to demand the return of his daughter Lyanna and justice for his son's honor, Aerys had him burned alive in his own armor while Brandon Stark strangled himself trying to reach a sword just out of his hands. The act, and Aerys's subsequent demand for Eddard Stark's and Robert Baratheon's heads, turned smoldering resentment into open rebellion within weeks.

As the rebel host closed on the capital in 283 AC, Aerys ordered his pyromancers to fire the wildfire caches beneath the city rather than surrender it, intending to leave nothing for the victors but ash. His own Kingsguard, Ser Jaime Lannister, cut his throat from behind on the Iron Throne's steps to stop it — an act that earned Jaime the name Kingslayer and haunted him the rest of his life, and that the smallfolk of King's Landing, had they known the alternative, would likely have thanked him for on the spot.