Demeter was born in Budapest, Hungary into a wealthy family that became impoverished following World War II and the rise of the Communist government. In 1956 at the age of 23, Demeter emigrated to Canada. He was among 200,000 refugees who escaped from the country after suppression of the Hungarian Revolution of 1956 by Soviet forces. By 1962, Demeter had started a successful career in Toronto as a land developer.