Stannis I Baratheon was King of Westeros and Lord of the Seven Kingdoms after claiming the throne during the War of Five Kings, re-instating the Baratheons as the ruling dynasty. He is sometimes known as "the Just" or "the Cursed"
Stannis I ruled from 303-334AC and is most remembered for casting aside the Faith of the Seven and instating R'hllor as the official religion of the Seven Kingdoms.
Under the counsel of the Red Priestess Melisandre of Asshai - who was rumoured to have become his paramour - Stannis I tore down the Great Sept of Baelor, with surviving members of the Houses that defied his claim being burnt alive at the heart of the sept's ruins; the single greatest sacrifice to the Lord of Light in known history.
The rest of his reign was notably uneasy, but due to his iron rule no major rebellions are known to have taken place. Stannis I died of natural causes at the age of nine-and-sixty - although there were rumours of weakening from the practice of dark magic - and was succeeded by his grandson, Edric Baratheon, as his daughter Shireen had died sometime beforehand of greyscale.
Later, after his death, two brothers would claim to be the bastards of King Stannis and the Lady Melisandre, taking the surname "Lighthart" in reference to their "father's" sigil.
Selyse Florent, wife (deceased)
Shireen Baratheon, daughter (deceased)
Edric I Baratheon, grandson (deceased)
Steffon Lighthart, claimed bastard (deceased)
Cyral Lighthart, claimed bastard (deceased)