Portrait of Maria Callas.

The North-American Maria Callas (soprano) was considered the biggest soprano of all times. Callas became famous not only by her voice -- which had unique characteristics --, but also by her personal life. By having a strong personality, now and then she got in fights with her colleagues, conductors, and patrons of concert halls around the world. The most iconic conflict may be the one with Rudolf Bing, from Met, who fired her after she refused to sing "La Traviata" and "Macbeth," both by Verdi, in alternate days. "La Traviata" and "Macbeth" have very different vocal demands. Answering to Bing, Callas sentenced that her voice wasn't an elevator.