Rabbenu Asher ben Yechiel (Rosh)

Rabbeinu Asher ben (or "bar") Yechiel was a prominent talmudic commentator, legal decisor, and one of the ba'alei hatosafot, that is an author of a tosafist commentary on the Talmud. He was born, lived, and taught in Germany, fleeing with his family to Spain after the imprisonment and death of his teacher, Maharam of Rothenburg. He served as a leading authority in Spain alongside Rashba. Due to the tremendous impact of his work, Hilkhot HaRosh, his halakhic authority was so widely regarded that he was one of three major rabbinic legal authorities whose work was selected by Rabbi Joseph Karo to serve as the basis of the decisions contained in his authoritative Beit Yosef and Shulchan Arukh.