Callas's voice was and remains controversial; it bothered and disturbed as many as it thrilled and inspired. Walter Legge stated that Callas possessed that most essential ingredient for a great singer: an instantly recognizable voice.During "The Callas Debate", Italian critic Rodolfo Celletti stated, "The timbre of Callas's voice, considered purely as sound, was essentially ugly: it was a thin sound, which gave the impression of dryness, of aridity.
Callas's voice has been difficult to place in the modern vocal classification or fach system, especially since in her prime, her repertoire contained the heaviest dramatic soprano roles as well as roles usually undertaken by the highest, lightest and most agile coloratura sopranos. Regarding this versatility, Maestro Tullio Serafin said, "This woman can sing anything written for the female voice".
Though adored by many opera enthusiasts, Callas was a controversial artist. While Callas was the great singer often dismissed simply as an actress. She considered herself first and foremost "a musician, that is, the first instrument of the orchestra.