Food for thought: Callas was first and foremost an ACTING singer, and was instrumental in transforming the world of opera from static singers to acting singers. As others have said her voice, as every other singer out there, had pros and cons. She was NOT a contralto (go listen to Marian Anderson or Kathleen Ferrier, for goodness'sake). What did happen is that a) she lost a lot of weight at one point because of personal life (Onassis), which is not neutral on the voice. And b) she sang probably too frequently, and often roles requiring very different qualities, which is why her career did not indeed last as long as some other singers out there.