Original: A number of classical composers have written incidental music for various plays, with the more famous examples including Ludwig van Beethoven's Egmont music, Franz Schubert's Rosamunde music, Felix Mendelssohn's music for A Midsummer Night's Dream, Georges Bizet's music for L'Arlésienne, and Edvard Grieg's music for Henrik Ibsen's Peer Gynt.
Simplified: A famous example is the incidental music for Shakespeare’s “A Midsummer Night's Dream” composed by Felix Mendelssohn in 1842.