Leitmotiv (leading motive). A term (often misspelt leitmotif) first used c.1865 by A. W. Ambros in article about Wagner operas and Liszt sym.-poems. ‘Representative theme’ is a good Eng. alternative. Composers throughout history have used the device in one form or another, e.g. Gluck and Mozart, Weber in Der Freischütz, Mendelssohn, Berlioz (the idée fixe in the Symphonie Fantastique), but it was raised to its highest and most complex form by Wagner, especially in Der Ring des Nibelungen, where the subtle combinations of leitmotiv create symphonic textures.

leitmotiv German word for a guiding theme in musical compositions. It is a theme that recurs throughout a work, usually an opera or a piece of programme music, and is evocative of an idea or a character on each occasion.