He is famous for two books of autobiographical memoirs Eleni and A Place for Us. The first describes the life of his family in Greece during the Second World War and Greek Civil War. The second relates their experiences as immigrants in 1950s America in the city of Worceste, Massachusetts.
In 1985 his story Eleni was made into a feature film starring John Malkovich as Gage.
Gage also worked as an Investigative Reporter for a number of years. During this period he covered the mafia. After his work with the mafia, he wrote a book, "The Mafia is not an Equal Opportunity Employer." The book covered the origin of the mafia and a history of the American mafia until 1970. It has since been revised and is now called "Mafia, USA."
He is also credited as an executive producer of Francis Ford Coppola's The Godfather III. Mr. Gage is a recipient of The International Center in New York's Award of Excellence.