She was a glamorous Greek opera star of singular talent and obvious vulnerability, and he was a charismatic, slightly sinister Greek tycoon. Both could really relate to each other because they shared itinerant difficult childhoods. The Greek émigré from Turkey was 19 years older than Callas, but he could not resist her quiet charms. A merchant's son from Turkey, he emigrated to Argentina, where he made a fortune importing tobacco, and then to New York, where he built his multimillion-dollar shipping business.

Callas too was the daughter of Greek immigrants, who simply stunned listeners with her precocious voice, later described by one of her teachers as ''violent cascades of sound, full of drama and emotion.'' Faced with bleak prospects in Greece, Maria returned to America, where she went broke in a fruitless effort to establish herself as an opera singer. She married a Veronese impresario 30 years her senior who sent her into her career as a world-renowned soprano.

Rendevous

Callas and Onassis were introduced in 1957 by a predatory social columnist Elsa Maxwell, one of a number of exotic secondary characters in the lovers' drama. The saga of Callas-Onassis began on a three-week cruise along the Greek and Turkish coasts in the summer of 1959. Though Onassis was then married to Tina Livanos, he seduced Callas on the cruise and the notorious affair began. After both lovers divorced their spouses, they alternately adored and raged at each other, even finding excitement in fisticuffs and thundering curses. ''What a woman!'' Onassis proclaimed after one exhausting battle.

The Greek idea that each person is half of what was once a whole and spends his or her whole life searching for the other individual who will make him complete really applied to their romance. He had the Oriental view that a real man does not allow himself to be conquered by love. Maria, on the other hand, flooded Onassis with her love, surrendered totally. She immersed herself totally in him and her restless and wandering nature found a kindred spirit in Onassis. On his part, her rich emotional life was what attracted Onassis in the first place.

But Callas was very sensitive, cautious, and shy about showing others her feelings. She had a craving for things which were far away and foreign or for things she had never experienced before. Towards the end she was pessimistic and inclined to feel emotionally depressed. She started withdrawing from everything.

Maria Callas's old-fashioned courtship and concept of a love relationship, to remain faithful to her loved one in good times and in bad, didn't quite gel with Onassis. She was always attracted to men older than her, someone who was emotionally mature and reliable and who could provide the security Maria desired. But sadly, Onassis could not be the father figure she sought everywhere.

Despite his best intentions Onassis always found his closest relationships rather tumultuous affairs in which some rather unlovely aspects of his, such as jealousy and the desire to dominate or to be a victim, kept showing their faces. These were never understood and never outgrown. He was also compulsively adventurous and unfaithful. Just before he was going to marry Jackie Kennedy, he called Callas asking her to come to Athens and ''save him,'' presumably by inciting a jealous Jackie to call off the wedding.

Tragedy and End

Callas lost her singing voice and Onassis suffered a series of tragedies -- the death of his only son and the suicide of his former wife -- as well as business reversals. The couple's devotion deepened, but she refused to be his lover as long as he remained married.

When Onassis was dying in 1975, he took Maria's final gift, a red cashmere Hermès blanket, to the hospital, although neither Maria nor his wife was with him at his death. A heartbroken Callas died two years later.