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).
The name was originally used among early Christians in honour of the saint, as opposed to the classical character. In England it was commonly spelled Ellen during the Middle Ages, and the spelling Helen was not regularly used until after the Renaissance. A famous bearer was Helen Keller (1880-1968), an American author and lecturer who was both blind and deaf.
This name has traditionally been more popular among Eastern Christians. In the English-speaking world it was not regularly used until the 19th century.