A powerful wizard who serves as Arthur's chief advisor. When Merlin was a child, King Vortigern was told that the boy's blood was necessary to keep his tower from constantly collapsing; however, Merlin identified a pool beneath the tower in which two dragons fought as the source of the instability. Some sources credit Merlin with constructing the Round Table as well as Stonehenge. Merlin's primary apprentice is the sorceress Morgan le Fay, Arthur's half-sister on his mother's side. Some sources have Merlin wind up trapped in an enchanted tomb (possibly in a cave, possibly in a tree) by a figure identified as Vivien or Nimue (the Lady of the Lake). In other tales, Merlin dies and is buried in the legendary forest Brocéliande.