Saints bearing the name include an 8th-century musician in the court of Charlemagne and an 11th-century French bishop who is the patron saint of brewers. It was also borne by Arnold of Brescia, a 12th-century Augustinian monk who rebelled against the Church and was eventually hanged. Famous modern bearers include American golfer Arnold Palmer (1929-2016) and Austrian-American actor and politician Arnold Schwarzenegger (1947-).
Due to its favourable meaning, this name was popular among early Christians, being borne by many early saints and four popes. It has been used in England since the Middle Ages, though it has been more popular in continental Europe. A notable bearer was the German composer Felix Mendelssohn (1809-1847).
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.