But alas, he (Gustav III) thought he was a great warrior king too, and he wasn't. The Swedish nobility became ever more dissatisfied with him, and in 1792 one of the angriest noblemen, Johan Anckarström, shot the king at a masque ball. Bang!
This, of course, was the inspiration for one of Guiseppe Verdi's operas, "Un Ballo in Maschera" (The Masked Ball), where, in a case of art imitating life, the king is assassinated at a masked ball.
Interesting bits of backstory on this opera:
1) Marian Anderson made her debut at the Metropolitan Opera in New York (she was the first black singer allowed on-stage there, in 1955) as Ulrica, the seer who prophesies that the king will be killed by his best friend.
Strangely enough, you don't see a lot of contraltos around anymore (Ulrica is a contralto). Not sure why.
2) When Verdi first wrote the opera, the censors had a conniption about the opera portraying a royal assassination. Verdi in turn then had an artistic conniption about the censors gutting his work.
They worked out a compromise. It wasn't going to be a king who was assassinated; it was going to be a governor. And he wouldn't be in Europe. Yes, folks, the Masked Ball was to be held in... *drums rolling* Colonial Boston. Yes, we all know that the Puritans had masked balls every weekend, because they were such party-hearty folk.
This example of total ludicrousness had everyone rolling their eyes at the time, and now, when the opera is staged, it's sensibly staged with a king being assassinated. In Europe. No Puritans or Bostonians in sight.