William Ewart Napier (17 January 1881, in East Dulwich, Surrey – 6 September 1952, in Washington, D.C.) was an American chess master of English birth.

He had his first successes with simultaneous games, among other things winning in December 1894 versus the acting United States Chess Champion Jackson Whipps Showalter.

In the same year he defeated the later grandmaster Frank James Marshall in a match, winning 7:1 with 3 draws.

At the beginning of 1899 Napier traveled to Europe, in order to study music there, and visited the chess clubs of London, Paris and Berlin.

In July 1904, he visited Great Britain and won a well-attended tournament in London against Richard Teichmann, Joseph Henry Blackburne and Isidor Gunsberg.

Napier called a game he lost to reigning World Champion Emanuel Lasker at Cambridge Springs 1904 the best of his career.