Alexander Onassis, American-Greek businessman (b. 1948)
Alexander Socrates Onassis (Greek: Αλέξανδρος Σωκράτης Ωνάσης; April 30, 1948 – January 23, 1973) was an American-born Greek businessman. He was the son of the Greek shipping magnate Aristotle Onassis and his first wife Tina Livanos. He and his sister Christina Onassis were upset by his father's marriage to Jacqueline Kennedy, and he was credited with attempting to improve the relationship between his father and Stavros Niarchos.

Born in New York City, Onassis was not formally educated and worked for several years for his father at his Monaco headquarters. The relationship between Onassis and his father experienced tensions as a result of his secret relationship with Fiona von Thyssen, former wife of Baron Hans Heinrich Thyssen-Bornemisza.

He was later appointed the head of Olympic Aviation, a Greek regional airline owned by his father. Onassis died in hospital as a result of injuries sustained in an air crash at Hellinikon International Airport at the age of 24. The Alexander S. Onassis Foundation was established in his memory.