Arthur is the name of the central character in Arthurian legend, a 6th-century king of the Britons who resisted Saxon invaders. He may or may not have been based on a real person. He first appears in Welsh poems and chronicles (perhaps briefly in the 7th-century poem Y Gododdin and more definitively and extensively in the 9th-century History of the Britons [1]). However, his character was not developed until the chronicles of the 12th-century Geoffrey of Monmouth [2]. His tales were later taken up and expanded by French and English writers.
The name came into general use in England in the Middle Ages due to the prevalence of Arthurian romances, and it enjoyed a surge of popularity in the 19th century. Famous bearers include German philosopher Arthur Schopenhauer (1788-1860), mystery author and Sherlock Holmes creator Arthur Conan Doyle (1859-1930), and science-fiction author Arthur C. Clarke (1917-2008).
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).
As a given name it was mostly masculine in America until around 2009. It was already rising in popularity for girls when singer Mariah Carey gave it to her daughter born 2011 (though this probably helped accelerate it).
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.
This name was later borne by three other English kings, as well as rulers of Scotland, Sicily (of Norman origin), the Netherlands and Prussia. Other famous bearers include William Wallace, a 13th-century Scottish hero, and William Tell, a legendary 14th-century Swiss hero (called Wilhelm in German, Guillaume in French and Guglielmo in Italian). In the literary world it was borne by dramatist William Shakespeare (1564-1616), poet William Blake (1757-1827), poet William Wordsworth (1770-1850), dramatist William Butler Yeats (1865-1939), author William Faulkner (1897-1962), and author William S. Burroughs (1914-1997).
In the American rankings (since 1880) this name has never been out of the top 20, making it one of the most consistently popular names (although it has never reached the top rank). In modern times its short form, Liam, has periodically been more popular than William itself, in the United Kingdom in the 1990s and the United States in the 2010s.