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).
As an English name, Caleb came into use after the Protestant Reformation. It was common among the Puritans, who introduced it to America in the 17th century.
The name was common among Jews in the Middle Ages, but it was not generally used as a Christian name in the English-speaking world until after the Protestant Reformation. It was moderately popular in the first half of the 20th century, but starting in the 1960s it steadily rose, reaching highs in the 1980s and 90s. The character Rachel Green on the American sitcom Friends (1994-2004) may have only helped delay its downswing.
Notable bearers include American conservationist Rachel Carson (1907-1964), British actress Rachel Weisz (1970-), and Canadian actress Rachel McAdams (1978-).