Fidelio is the name of an opera with spoken dialogue by Ludwig van Beethoven. His only opera, it was written on a libretto by Joseph Sonnleithner. The story tells how Leonore rescues his husband for political prision, disguised as a guard named 'Fidelio'. The opera underwent many transformations and caused Beethoven many difficulties from an artistic standpoint, with the first and second versions (1804 and 1085) being notably unsuccesful, and the third and final version (1814) achieving success after many revisions and rewritings. Nowadays, the 1814 version is currently referred to as Fidelio, while the others are, by convention, reffered to as Leonore. Likewise, the opera had four versions of its overture, with Beethoven rewriting the entire music at one point. The overtures are now known as Leonore no. 1, Leonore no. 2, Leonore no. 3, and Fidelio. Until the middle of the 20th century, it was common practice to introduce Leonore no. 3 as a musical break between the two scenes of Act II.