Heinrich was popular among continental royalty, being the name of seven German kings, starting with the 10th-century Henry I the Fowler (the first of the Saxon kings), and four French kings. In France it was usually rendered Henri from the Latin form Henricus.
The Normans introduced the French form to England, and it was subsequently used by eight kings, ending with the infamous Henry VIII in the 16th century. During the later Middle Ages it was fairly popular, and was generally rendered as Harry or Herry in English pronunciation. Notable bearers include arctic naval explorer Henry Hudson (1570-1611), American-British novelist Henry James (1843-1916), American automobile manufacturer Henry Ford (1863-1947), and American actor Henry Fonda (1905-1982).
An influential bearer of the name was Martin Luther (1483-1546), the theologian who began the Protestant Reformation. The name was also borne by five popes (two of them more commonly known as Marinus). Other more recent bearers include the German philosopher Martin Heidegger (1889-1976), the American civil rights leader Martin Luther King Jr. (1929-1968), and the American filmmaker Martin Scorsese (1942-).
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.