Tweedledum and Tweedledee

Tweedledum and Tweedledee are fictional characters in an English nursery rhyme and in Lewis Carroll's Through the Looking-Glass, and What Alice Found There. Their names may have originally come from an epigram written by poet John Byrom. The nursery rhyme has a Roud Folk Song Index number of 19800. The names have since become synonymous in western popular culture slang for any two people who look and act in identical ways, generally in a derogatory context.