Aristotle Onassis (Αριστοτέλης Ωνάσης) (January 15, 1906–March 15, 1975) was the most famous Greek shipping magnate of the 20th century.

Onassis was born in Smyrna, Ottoman Empire (now Izmir, Turkey). At the time of his birth, Smyrna had a significant Greek population. After being briefly occupied by Greece (from 1919 to 1922), in the aftermath of the allied victory in WW1, the city was recaptured by Turkey, and the Onassis family holdings were lost, spurring them to move to Greece as refugees. By 1932, Onassis had become a world-class businessman, owning commercial ships, tankers and whalers. He founded Olympic Airways (today Olympic Airlines), the Greek national carrier, in 1957. In 1954, the FBI investigated Onassis for fraud against the U.S. government. He was charged with violating the citizenship provision of the shipping laws which requires that all ships displaying the American flag be owned by United States citizens. Onassis pled guilty and paid $7 million.

He married Athina Mary Livanos , daughter of shipping magnate Stavros Livanos , on December 28, 1946; their son, Alexander (April 30, 1948–January 23, 1973), and daughter Christina Onassis, were born in New York City. After their divorce, Athina married her late sister's widower—and Onassis's arch shipping rival—Stavros Niarchos .

Despite the fact they were both married, Onassis and opera diva Maria Callas embarked on a notorious affair. According to Greek Fire: The Story of Maria Callas and Aristotle Onassis by Nicholas Gage, Callas gave birth to their child, a boy, who died hours later on March 30, 1960. Onassis cruelly broke with Callas to marry Jackie Kennedy, the widow of U.S. President John F. Kennedy, on October 20, 1968.

Onassis died in Neuilly-sur-Seine, France of bronchial pneumonia at the age of 69. Alexander had died in an airplane crash. Christina inherited his fortune, which has since passed to her only child, Athina Roussel.