Rabbi Zerachiah the Greek (in Hebrew, Zerachiah ha-Yavani or ha-Yewani; sometimes known by the acronymistic nickname "Ra'Za'H") was a Greek-Jewish ethicist who resided in the Byzantine Empire in the thirteenth or fourteenth century. Of his life no details are known, except that he was the author of an ethical work entitled Sefer ha-Yashar (not to be confused with the many other Jewish writings of the same name); this work was confused with Jacob Tam's halakhic work of the same name and erroneously attributed to the renowned tosafist. This error was detected by Menahem Lonzano, who, in his poem "Derek Ḥayyim" ("Shete Yadot," p. 122), expressly states that the ethical work in question belonged to Zerahiah. Lonzano did not succeed, however, in correctly establishing the identity of its author