Robert Leiber, S.J. (10 April 1887 – 18 February 1967) was a close advisor to Pope Pius XII, a Jesuit priest from Germany, and Professor for Church History at the Gregorian University in Rome from 1930 to 1960. Leiber was, according to Pius's biographer Susan Zuccotti, "throughout his entire papacy his private secretary and closest advisor".[1]