Uther Pendragon was brother to Ambrosius. Uther Pendragon became King of Britain on his brother's death. Uther Pendragon is the father of Arthur.
Geoffrey of Monmouth says that Arther was conceived at Tintagel, when Uther Pendragon used Merlin's magic to deceive Ygerna into sleeping with him. Monmouth translates Pendragon as "dragon's head", the name could equally well mean the "head dragon" (high tribal leadership). Uther Pendragon exists with this title in in some early Welsh poetry, well before Geoffrey wrote his stories.
Local lore assocates Pendragon Castle, four miles south of Kirkby Stephenin Cumbria, with Uther Pendragon. The castle is not from the era of Uther Pendragon, it is a Norman castle built by Hugh de Morville in the 12th century. There seems to be no evidence for or against a earlier castle on the site. One story tells of how Uther was killed here with one hundred of his men when Saxon dogs poisoned the well. Another retells an attempt by Uther Pendragon to divert the nearby River Eden to create a moat for this castle.