Due to the saint's popularity, the name came into general use in medieval Europe, especially in Spain and France. It was also borne by a 16th-century king of Portugal who died in a crusade against Morocco.
Geoffrey based parts of Merlin's character on Myrddin Wyllt, a legendary madman and prophet who lived in the Caledonian Forest. Other parts of his life were based on that of the historical 5th-century Romano-British military leader Ambrosius Aurelianus (also known as Emrys Wledig). In Geoffrey's version of the tales and later embellishments Merlin is a magician and counselor for King Arthur.
In the United States it became more common for girls in the early 1980s, shortly after the debut of the television sitcom The Facts of Life (1979-1988), which featured a character named Blair Warner. The name left the American top 1000 rankings two decades later, but was resurrected by another television character, this time Blair Waldorf from the series Gossip Girl (2007-2012).