Gruber was born in New York City in 1930. He was the son of German-American doctor Fredrick Gruber and his wife Maria. Franz attended Columbia University and graduated in 1949. After getting a job as a journalist for The New York Times, Franz traveled to Japan to wrote about Japanese culture and religion. In 1957, he starting his filming career and played the foreign character in many kaiju films. His acting career lasted from 1963 to 1974. Returning to the USA, he became a teacher at Brooklyn College Academy until he retired in 1989. He married Jennie Rosa in 1955 and has two children.