Fiona Frances Elaine Campbell-Walter, formerly Baroness Thyssen-Bornemisza de Kászon et Impérfalva, is a New Zealand-born British model. She had a successful career in the 1950s and was photographed by Henry Clarke and Cecil Beaton. Campbell-Walter was known for her relationship with Greek shipping heir Alexander Onassis, whom she began an affair with after separating from her husband, Baron Hans Heinrich Thyssen-Bornemisza de Kászon et Impérfalva.