First performed in 1859, "A Masked Ball", or in the original Italian "Un Ballo in Maschera" is an opera by the legendary Italian composer Giuseppe Verdi (1813-1901).

Quite a few stage works have different versions, but this one is unusual in having two versions with completely different geographical settings. The original version was set in Sweden, and based on a real historical event - the assassination of King Gustav III (1746-1792). However, this was to prove controversial. At that time Italy was in a state of political turmoil, and the censors were concerned that a stage portrayal of an actual monarch being assassinated in the not too distant past might stoke insurrection. This led to Verdi and his librettists creating an alternative version set suitably far away, in Boston in the USA during the colonial era. There was also a proposed third version, set in Stettin, in present-day Poland, but that fell by the wayside.

It's not only the matter of a regicide that made the opera controversial, but also the hints that the King may well have been gay, though these were decidedly toned down from the source material.

Nowadays, although both versions remain in the repertoire, the original Swedish version is the one most often performed, and although it has never quite achieved the popularity of "Aida" or "La Traviata", it is a well-loved and familiar work.

More Info: en.wikipedia.org