János Ruff, S.J., Ph.D. (Hajós, February 12, 1915 – Munich, Germany, October 31, 1992) was a Jesuit priest, Roman Catholic priest, philosophy professor, theologian, and missionary. He spent a significant part of his life in Latin America, where he taught philosophy in Brazil for more than twenty years and participated in Jesuit priestly formation. Later, he served in Germany as a chaplain and hospital minister. He belonged to that generation of 20th-century Hungarian Jesuit émigrés who continued their religious and scholarly work abroad after the communist takeover.

He was born in Hajós on February 12, 1915. He completed his secondary education at the Jesuit high school in Kalocsa, then entered the Society of Jesus in Budapest on July 30, 1935. He completed his novitiate and rhetoric training at Manréza in Zugliget, after which he studied philosophy in Budapest from 1938 to 1941. He spent the practical phase of his Jesuit training—the magisterium—between 1941 and 1943 at the Pius High School in Pécs, where he served as a teacher and formator. He then continued his theological studies in Szeged; he was ordained a priest there on July 26, 1946. He earned a doctorate in philosophy from the University of Szeged in 1948, while having already served as a philosophy teacher for the Jesuit scholastics at Manréza in Budapest since 1947.

As a result of the communist persecution of the Church, he was forced to leave Hungary in 1949. He went to Italy, where he continued to teach philosophy to Hungarian Jesuit novices in Chieri. He then completed the final stage of Jesuit formation—the third probation—in Florence, and from 1951 to 1953 pursued two years of advanced studies in Rome. In 1953, he moved to Innsbruck, where he taught philosophy before being assigned to a mission in South America.

In 1954, he was sent to Brazil, where he devoted the next twenty-plus years to Jesuit higher education and priestly formation. He taught philosophy and served as a librarian in São Leopoldo, and later taught in Rio de Janeiro and São Paulo as well. Throughout his career, he introduced generations of seminarians and young Jesuits to philosophical thought, while also being an active participant in the Order’s scholarly life. His work in Brazil constitutes a significant chapter in the Latin American mission of the Hungarian Jesuits.

In 1975, his superiors recalled him to Europe. In Schrobenhausen, Bavaria, he first became the chaplain for the community of the English Ladies (Congregatio Jesu), and later served as chaplain at the local hospital. In this role, he devoted special care to the spiritual accompaniment of the sick, the elderly, and the dying, which became the defining ministry of the last decade and a half of his life.

In 1992, he was diagnosed with a serious form of cancer. He spent the final weeks of his life in the infirmary of the Berchmanskolleg in Munich, surrounded by his fellow religious. He passed away in Munich on October 31, 1992.