It is sung by Calaf, il principe ignoto (the unknown prince), who falls in love at first sight with the beautiful but cold Princess Turandot. "Nessun dorma" is an aria from the final act of Giacomo Puccini's opera Turandot and one of the best-known tenor arias in all opera. In the aria, Calaf expresses his triumphant assurance that he will win the princess.

Any man who wishes to wed Turandot must first answer her three riddles; if he fails, he will be beheaded.