The Mountebanks is a comic opera in two acts with music by Alfred Cellier and Ivan Caryll and a libretto by W. S. Gilbert. The story concerns a magic potion that causes the person to whom it is administered to become what he or she has pretended to be. It is similar to several "magic lozenge" plots that Gilbert had proposed to the composer Arthur Sullivan, but that Sullivan had rejected, earlier in their careers. To set his libretto to music, Gilbert turned to Cellier, who had previously been a musical director for Gilbert and Sullivan and had since become a successful composer. During the composition of the piece Cellier died, and the score was finished by the original production's musical director, Ivan Caryll, who became a successful composer of Edwardian Musical Comedy.