Zacharias Ursinus (1534 - 1583) was born Zacharius Baer in Breslau. He gave himself the nickname ursus, meaning bear, by which he is best known. He entered Wittenberg University, boarding with Melanchthon, the successor to Martin Luther. He then studied in Strasbourg, Basel, Lausanne and Geneva. He then went to Heidelberg as professor of theology but was expelled when political power changed. While at Heidelberg, Ursinus (28 years old) and Caspar Oleviantus (26 years old) wrote the 129 questions and answers that constitute the Heidelberg Catechism.