One of the greatest coloratura opera singers of the 20th century, Maria Callas defined the term "diva" in all of its connotations. An enormously gifted performer from an early age, her versatility allowed her to tackle a wide variety of operas, from the powerful dramas of Richard Wagner to bel canto and the classical opera seria style. But a difficult childhood had left her with a volcanic personality that often resulted in clashes with opera houses, fellow performers and the press, which dubbed her as temperamental. An ill-fated love affair with Greek tycoon Aristotle Onassis also brought its share of headlines and heartache. By the end of the 1950s, loss of vocal power, caused by either dramatic weight loss or simple wear from the rigors of singing, led to a decline in her career that largely ended in 1965, save for a nostalgic tour in 1973. Her death in 1977 enshrined her as a larger-than-life figure whose emotional highs and lows often obscured the fact that she was one of opera's greatest interpreters, as well as one of its best-selling artists, even decades after her death.