For 10 points, name this mentor of King Arthur, a great wizard.
Based on a figure who went mad after the death of his king Gwendelou and fled into the wood, Geoffrey of Monmouth created the first legends of this figure. As a boy called "Ambrosius," this figure told Vortigern about red and white dragons fighting below a tower. This figure was the child of an incubus and a peasant, and this figure (*) disguised Uther Pendragon so he could woo Ygraine. This figure was trapped in a tree by the Lady of the Lake using his own powers, and this figure gave the prophecy that whoever drew the Sword in the Stone would be king of Britain. For 10 points, name this mentor of King Arthur, a great wizard.
Based on a figure who went mad after the death of his king Gwendelou and fled into the wood, Geoffrey of Monmouth created the first legends of this figure.
Merlin