What was the name of King Arthur's father?

Uther Pendragon is a legendary King of Britain; and, it is generally accepted that Uther Pendragon is the father of King Arthur. Uther's biography as first written down by Geoffrey of Monmouth in his Historia Regum Britanniae (History of the Kings of Britain) has him associated with Arthur and includes him as his father.

Arthur was called an illegitimate child (though later legend emphasizes that his conception occurred after King Gorlois's death) and that he was legitimated by King Uther's subsequent marriage to Igrain.

The details of Arthur's story are mainly composed of folklore and literary invention. His historical existence is still debated and disputed by modern historians. The sparse historical background of Arthur is gleaned from various sources. They include: the Annales Cambriae, the Historia Brittonum, and the writings of Gildas. King Arthur's name also occurs in early poetic writings.