Rigoletto is an opera composed by the Italian Giuseppe Verdi in the 19th century.
One of the most famous songs from the opera is La donna è mobile, which was sung by the Doctor on several occasions and analyzed by Data in 2368. (TNG: "A Matter of Time"; VOY: "Tinker Tenor Doctor Spy", "Life Line")
In late 2377, while on an away mission aboard the Delta Flyer together with Captain Kathryn Janeway, the Doctor performed another song from the opera, Questa o quella. (VOY: "Renaissance Man")