tweedledum (n.)

paired with tweedledee to signify two things or persons nearly alike, differing in name, 1725, coined by English poet John Byrom (1692-1767) in his satire "On the Feud Between Handel and Bononcini," a couple of competing musicians, from tweedle "to sing, to whistle" (1680s), of imitative origin. The -dum and -dee perhaps suggest low and high sounds respectively.