The Alexander S. Onassis Foundation (Greek: Κοινωφελές Ίδρυμα Αλέξανδρος Σ. Ωνάσης), commonly known as Onassis Foundation (Greek: Ίδρυμα Ωνάση) is a public benefit foundation based in Vaduz, Liechtenstein. It was established by Aristotle Onassis in his will in Liechtenstein in order to honor the memory of his son Alexander, who died at age 24 in an airplane crash in 1973.