Program music
Franz Liszt made programme music very popular in his symphonic poems.  Hector Berlioz's Symphonie Fantastique describes a story he made up himself about a man who has dreams about a woman he loves.  The woman he loves is represented by a tune (melody) which is heard in different ways during the symphony.  It is called an idée fixe (French for "fixed idea").  This way of linking a theme (tune) with a person led to Wagner's use of leitmotif in his operas in which a tune is linked to a person, event or idea.  At the start of the 19th century Richard Strauss  wrote several symphonic poems, often using a leitmotif to describe the person it is about.  They include Don Juan, Don Quixote and Ein Heldenleben (A hero's life).