In esoteric terms, the Red Dragon, Ddraig Goch, represents the sovereignty of Britain, and is the totem beast of the greatest line of Kings, the Pen-Dragons.  The Red Dragon (dragon is ddraig in Welsh) is derived from the Great Red Serpent that once represented the Old Welsh God, Dewi, who later metamorphosed into Wales' mythical patron saint, David.

There is a legend that Merlin, Druid Wizard and later resident Wiseman of King Arthur's court, was called to help King Vortigern.  He was attempting to build a temple (Stonehenge) on Salisbury Plain, but the structure kept falling down.  Merlin saw that the problem was that a Red and White Dragon were fighting in a mystical pool beneath the temple's foundations. Stonehenge, a Megalithic Stone Circle dating from the 3rd Millennium, B.C.E., is built on a powerful convergence of earth energy lines (Ley Lines), represented by the two Dragons.

Merlin prophesied that Vortigern, the Red Dragon, would be slain by Uther Pendragon, the White Dragon, and so it happened...