A Composite with No Single Original

Merlin as he is known today is a literary composite rather than the record of one figure. Geoffrey of Monmouth, who introduced him to wide readership in the twelfth century, appears to have fused a Welsh tradition of a wild prophetic madman named Myrddin Wyllt, said to have gone insane after a battle and lived as a hermit uttering prophecies in the forest, with a separate earlier figure, Ambrosius Aurelianus, a shadowy post-Roman British leader mentioned in older sources. Geoffrey renamed his combined figure Merlinus, likely to avoid an unfortunate resemblance between Myrddin and a Latin obscenity, and gave him the role of prophet and enchanter attached to Arthur's court that has stuck ever since.

Later medieval writers kept building on this base rather than drawing on any single stable source: Robert de Boron added the account of Merlin's demonic parentage and his role in arranging Arthur's conception and the Round Table, and Thomas Malory's fifteenth century synthesis combined these accretions into the version most modern retellings still follow. The result is a figure assembled in layers across several centuries and several independent literary traditions, Welsh prophetic legend, Galfridian pseudo-history, French romance invention, with no single original Merlin behind them that scholarship can point to and call the source.