Don Carlos
From Memory Alpha, the free Star Trek reference
Don Carlos is an opera composed by Giuseppe Verdi in the 19th century.
In early 2375 the Doctor wanted to rehearse a duet from Don Carlos on the holodeck, but it was still occupied by Tom Paris running his Captain Proton holoprogram. (VOY: "Night")
The Doctor performed a duet from the opera, Dio, che nell'alma infondere, aboard the USS Voyager for an audience of Voyager crew members and a number of fascinated Qomar. He later gave small holograms of him singing the same song to Qomar admirers, even singing a duet with his small holographic self. (VOY: "Virtuoso")
