Maria Callas was an American opera singer in the 20th century. Since he was annoyed by Giuseppina Pentangeli's character after performing "O, soave fanciulla" with her, The Doctor considered singing a duet with Maria Callas the next time. (VOY: "The Swarm") According to the Star Trek Encyclopedia (4th ed., vol. 1, p. 114) , the birth and death years of Maria Callas were 1923 and 1977, respectively. This source said that Ms. Callas "revived classical coloratura roles in the mid-20th century with her lyrical and dramatic versatility."