First born of Lord Steffon Baratheon and Cassana of House Estermont, born at Storm's End in 262 AC and fostered as a boy at the Eyrie under Lord Jon Arryn alongside Eddard Stark, the two wards growing as close as any sons of the same father. In 278 AC his parents were drowned within sight of Storm's End when their carrack Windproud foundered in Shipbreaker Bay returning from a fool's errand to Volantis, leaving Robert lord of his house at sixteen with his brothers Stannis and Renly in his keeping. He came in time to be betrothed to Lyanna Stark, the willful sister of his fostered brother, and at the great tourney at Harrenhal in 281 AC bore the slight of watching her crowned queen of love and beauty by his cousin Prince Rhaegar Targaryen, a passing insult that he carried like a brand long after the prince stole her away the following year.
Lord Rickard Stark and his heir Brandon rode to King's Landing demanding her return and were burned and strangled in the throne room for the asking, after which mad King Aerys II called for the heads of his own wards. Lord Arryn raised his banners instead, and Robert rallied the stormlands. He slew Lord Marq Grafton at Gulltown to break the loyalist blockade of the Vale, took three of his own bannermen captive at the Battle of Summerhall in a single morning's fighting and won two of their houses to his cause by sparing them, lost the Battle of Ashford to Lord Randyll Tarly's van but kept the bulk of his host, and was hunted half-dead through the riverlands by his cousin Lord Jon Connington until he took refuge in a brothel in Stoney Sept, where the smallfolk hid him while Lord Eddard and Lord Hoster Tully marched to relieve him in the Battle of the Bells. At the ruby ford of the Trident in 283 AC, with the rebellion's fate hung on a single ford, Robert met Prince Rhaegar in the river in single combat and crushed his ruby-studded breastplate with his warhammer, the prince's rubies scattered along the stones of the ford for years to come.
He was crowned in late 283 AC, took Lord Arryn as his Hand on the grounds that he had been a second father to him, and wed Cersei Lannister to bind her father Tywin's loyalty to his throne — three children of her body were named his heirs, though all three were got of her twin brother Ser Jaime Lannister, as the realm would only come to learn after his death. He named his brother Renly to Storm's End and Stannis to Dragonstone, the latter a slight Stannis never forgave him for. After putting down the Greyjoy Rebellion in 289 AC at the Siege of Pyke he gave himself to feasting, drink, whoring, and the hunting that he had always loved best, and the king who had killed Rhaegar at the Trident grew fat in his silks with no battle left to fight. When Lord Arryn died suddenly in 298 AC Robert rode north to Winterfell to name his old friend Eddard the new Hand of the King, and rode home to King's Landing with the Stark girls and the boy prince in his train; some months later he was gored open by an enormous boar while hunting in the kingswood, his guts spilled out over his saddle by his own carelessness with a wineskin, and he died upon a bed in the Red Keep at the dawn of A Game of Thrones, his last act to name Lord Eddard Protector of the Realm.