After Aegon Targaryen conquered the Seven Kingdoms of Westeros, the Iron Throne was forged from the swords of Aegon's defeated enemies during the War of Conquest. These blades were melted down by the breath of the mighty dragon Balerion, and then adjusted to a throne of daunting size and appearance. The chair is cold and hard, with many jagged edges due to the blades.
Despite representing the monarchy of the Seven Kingdoms, the Iron Throne is the most uncomfortable seat for any king or Hand of the King to sit on. Aegon believed that this should serve as a moral lesson to his future heirs that no ruler should be seated upon a throne carelessly.
During the reign of the Mad King Aerys II, his increasing insanity caused him to spend most of his time siting on the throne, often cutting himself. He has often been referred to as "King Scab" because of it. After the War of the Usurper, Robert Baratheon became the new king of Westeros and seated himself upon the Iron Throne.