This might be obscure for some people, but Ludwig von Beethoven wrote one opera in OTL called
Fidelio for which he wrote four overtures! According to Matthew Boyden's
The Rough Guide to Opera, however, the composer had planned to work on many more:
"[After 1814], Beethoven considered [...] a work based on
Macbeth (abandoned because his librettist thought it too gloomy) and a lyrical opera to be titled
Bacchus. At regular intervals he approached George Friedrich Treitschke--his collaborator on the last rewrite of
Fidelio--with various ideas, including operas to be titled
The Ruins of Babylon and
Romulus. Most ambitiously, he wrestled with a setting of both parts of Goethe's
Faust, a project on which he began work in 1809 and continued until his death [...] it got no further than sketches." (122-3).
If he had completed them before his death in 1827, how would these works have been received during his life, and how might they shape his reputation in the future?