masc. proper name, Old Testament eldest son of Jacob and name of the tribe descended from him, from Greek Rouben, from Hebrew Reubhen, probably literally "Behold a son," from reu, imperative of ra'ah "he saw" + ben "a son."
As a typical name of a farmer, rustic, or country bumpkin, from 1804. The Reuben sandwich of corned beef, sauerkraut, etc., on rye bread, an American specialty (1956) is the same name but "Not obviously connected" with the "country bumpkin" sense in rube [OED], but is possibly from Reuben's restaurant, a popular spot in New York's Lower East Side. Various other Reubens have been proposed as the originator.
1940, in reference to U.S. cartoonist Reuben Lucius Goldberg (1883-1970) who devised fantastically complex gadgetry to accomplish simple tasks. His British counterpart was Heath Robinson (1872-1944).