Hennig, Paul Gottfried Johannes (John) (1911–86), scholar and businessman, was born 3 March 1911 in Leipzig, Germany, fourth of five children of Fürchtegott Max Hennig, protestant theologian and teacher, and his wife Berta Johanna (neé Clemen) who was from a family of distinguished academics (her brothers Carl and Paul were professors at Bonn University, and her brother Otto, a close friend of Max Hennig, was a professor at Leipzig University). Hennig attended (1920–28) the famous Thomas School in Leipzig. He studied theology, philosophy, history, and modern languages at the universities of Bonn (1929–30), Berlin (1930–31), and Leipzig (1931–3), attending lectures by, among others, E. R. Curtius, E. Rothacker, Theodor Frings and Theodor Litt. In 1933 Leipzig University awarded him a doctorate for his dissertation Lebensbegriff und Lebenskategorie. Studien zur Geschichte und Theorie der geistesgeschichtlichen Begriffsbildung (‘The concept and category of life. Studies in the history and theory of concept formation in the humanities’).
In 1933 Hennig married Kläre (Claire) Meyer (b. 1907), daughter of the industrialist and inventor Felix Meyer and his wife Marguerite Darmstaedter, liberal German Jews who lived in Aix-la-Chapelle. They were to have three daughters: Gabriele, Monica, and Margot. With the rise of the Nazis, and given his marriage to Kläre, Hennig's ambition to pursue an academic career became hopeless so he took up a position in his father-in-law's firm, ROTA Werke, later becoming the director, since his father-in-law had officially to pass the management over to a non-Jew.
Hennig converted from protestantism to catholicism in 1936. After the pogrom in 1938, and as ever stricter anti-Jewish laws put the families in imminent danger, Hennig managed in 1939 to get his family into Belgium and proceeded from there to Dublin, ahead of his family who followed six weeks later – some of a very limited number of refugees to be allowed into the country. This had become possible through a contact with an Irish Jesuit from Belvedere College who offered him a temporary teaching position there. On arrival in Ireland Hennig changed his first name to ‘John’, which he kept for the rest of his life. The family lived in Dublin (Clontarf and Sutton) from 1939 to 1956. He taught German at Belvedere College (1939–45), and also taught part-time at Maynooth (1943–46) and UCD. He supplemented his meagre income by giving private lessons in German, through his journalism, and by delivering talks. The family also got some small support from the royalties for the patents of his father-in-law F. Meyer, paid by the British firm Johnson & Jorgensen.
Hennig became a naturalised Irish citizen in 1945. After the war he made a living as records officer in the library and records section of Bord na Móna, and carried out a comprehensive study of world literature on current turf production and utilisation techniques and the latest advances in machine design. From 1948 he held a similar position as archivist for the ESB. During his time in Ireland Hennig was an exceptionally prolific author, writing and publishing widely in various areas, particularly theology (liturgical studies), philosophy, history, medieval studies, and the history of the church. His articles appeared in over thirty journals and magazines, plus numerous newspapers. He was elected a member of the RIA in 1947. He socialised with other exiles such as Ludwig Bieler (qv), Erwin Schrödinger (qv), and Hans Sachs, and counted among his Irish friends and acquaintances Frank Gallagher (qv), Evie (qv) and Joseph Hone (qv), Arland Ussher (qv), Arthur Cox (qv), and William (‘Billy’) O'Sullivan.
Hennig and his family left Ireland in 1956 for Basle, Switzerland. There he took up again a managing position in his father-in-law's firm, which in the meantime had been moved to Öfflingen, Germany, near the Swiss border. Hennig actively pursued his liturgical and philosophical studies further and renewed his friendship with the philosopher Karl Jaspers, who was a professor at Basle University and whom he had known since his days in Aix-la-Chapelle. In 1967 Hennig was voted an extraordinary member of the Abt-Herwegen Institut für Liturgische und Monastische Forschung at the monastery of Maria Laach. He was awarded an honorary doctorate by the Philosophical-Historical Faculty of Basle University in 1970. Hennig did not return to Ireland and died in Basle on 11 December 1986, where he was buried. His literary bequest is held in the Exilarchiv, Deutsche Bibliothek Frankfurt.
Hennig's primary significance in relation to Ireland is his research and writing relating to Irish–German studies. He did ground-breaking research in that area and continues to be of great influence and importance. His stay in Ireland helped him to become the specialist in ‘Irlandkunde’ (a term he coined). A bibliography of his works containing some 900 entries appeared in Archiv für Liturgiewissenschaft in 1971, 1978, and 1986. His articles have been collected in several publications, among them Goethe and the English-speaking world (1988); Medieval Ireland, saints and martyrologies, ed. M. Richter (1989), and Exil in Irland: John Hennigs Schriften zu deutsch–irischen Beziehungen, ed. G. Holfter and H. Rasche (2002). Die bleibende Statt is a privately published autobiographical account of his emigration, wartime and post-war experiences.