Imprisoned by the Lady of the Lake, this wise man is sometimes credited with designing the Round Table.
This legendary figure helped Igraine conceive her son and directed the building of Stonehenge. As a child, this man revealed that King Vortigern's castle has been built on a pair of sleeping dragons, and foretold that Britain will be ruled by (*) Uther Pendragon. Imprisoned by the Lady of the Lake, this wise man is sometimes credited with designing the Round Table. For 10 points, name this wizard, an advisor to King Arthur.
This legendary figure helped Igraine conceive her son and directed the building of Stonehenge.
Merlinus Ambrosius (accept Myrddin Emrys; prompt on Emrys or Ambrosius)