Oluf (Olaus) Gerhard Tychsen (December 14, 1734, Tønder, then Schleswig, now Denmark – December 30, 1815, Rostock, then Mecklenburg-Schwerin, now Germany) was a German Orientalist and Hebrew scholar. He is known today as one of the founding fathers of Islamic numismatics.
As a Lutheran Christian, he attended the Christianeum grammar school in Altona, then Holstein and the rabbinic school attached to the Altona Ashkenazi synagogue, led by Jonathan Eybeschütz, chief rabbi of the Threesome Qehilla Altona-Hamburg-Wandsbek. From 1756 he studied Oriental languages at the University of Halle.
He spent a year of missionary work towards the conversion of Jews, and then taught Hebrew in the newly founded University of Bützow. He held librarian and academic positions in Bützow. There he founded the Journal Bützower Nebenstunden, which comprised a broad variety of articles about the Old Testament and Oriental Culture, especially material culture, such as Islamic coins.
From 1778 he taught at the University of Rostock and led the Rostock University Library. He worked in different fields of Oriental studies, Arabic, Syriac, and Hebrew. His Introduction into Islamic Numismatics, in 1794, was the first scientific handbook on this topic, based on twenty-seven years of research. Among his students were Christian Martin Frähn, later professor at the University of Kazan and later founder of the Asiatic Museum in Saint Petersburg, and Christian Adler, who wrote the first scientific catalogue of a collection of Islamic coins and later became superintendent for Schleswig-Holstein. He was a prolific author who published some forty volumes of scholarly studies during his academic career. As the only known of a non-Jew, he received rabbinic ordination.