Mata Hari was a Dutch exotic dancer and courtesan who was also a SPY during World War I. Her real name was Margaretha Geertruida Zelle, but she was known by her stage name, Mata Hari. She was convicted of espionage and executed by firing squad in France in 1917. The crossword solutions for the term 'Mata Hari Was One' are 'SPY' (3 letters) and 'ALIAS' (5 letters). This accurately describes Mata Hari's role as a SPY and her use of an ALIAS to conceal her identity.