Uther Pendragon - History of The Kings of Britain

Uther is best known from Geoffrey of Monmouth's History of the Kings of Britain (1136) where he is the youngest son of King of Britannia Constantine II. His eldest brother Constans succeeds to the throne on their father's death, but is murdered at the instigation of his adviser Vortigern, who seizes the throne. Uther and his other brother Aurelius Ambrosius, still children, flee to Brittany. After Vortigern's alliance with the Saxons under Hengist goes disastrously wrong, Aurelius and Uther, now adults, return. Aurelius burns Vortigern in his castle and becomes king.

With Aurelius on the throne, Uther leads his brother in arms to Ireland to help Merlin bring the stones of Stonehenge from there to Britain. Later, while Aurelius is ill, Uther leads his army against Vortigern's son Paschent and his Saxon allies. On the way to the battle, he sees a comet in the shape of a dragon, which Merlin interprets as presaging Aurelius's death and Uther's glorious future. Uther wins the battle and takes the epithet "Pendragon", and returns to find that Aurelius has been poisoned by an assassin. He becomes king and orders the construction of two gold dragons, one of which he uses as his standard. He secures Britain's frontiers and quells Saxon uprisings with the aids of his retainers, one of whom is Gorlois, Duke of Cornwall. At a banquet celebrating their victories Uther becomes obsessively enamoured of Gorlois' wife, Igerna (Igraine), and a war ensues between Uther and his vassal. Gorlois sends Igerna to the impregnable castle of Tintagel for protection while he himself is besieged by Uther in another town. Uther consults with Merlin who uses his magic to transform the king into the likeness of Gorlois and thus gain access to Igerna at Tintagel. He spends the night with her and they conceive a son, Arthur, but the next morning it is discovered that Gorlois had been killed. Uther marries Igerna and they have another child, a daughter called Anna (in later romances she is called Morgause and is usually Igerna's daughter by her previous marriage). Morgause later marries King Lot and becomes the mother of Gawain and Mordred. Uther later falls ill, but when the wars against the Saxons go badly he insists on leading his army himself, propped up on his horse. He defeats Hengist's son Octa at Verulamium (St Albans), despite the Saxons calling him the "Half-Dead King." However, the Saxons soon contrive his death by poisoning a spring he drinks from near Verulamium.

Uther's family is based on some historical figures; Constantine on the historical usurper Constantine III, a claimant to the Roman throne from 407–411, and Constans on his son. Aurelius Ambrosius is Ambrosius Aurelianus, mentioned by Gildas, though his connection to Constantine and Constans is unrecorded.