REISCHER, JACOB BEN JOSEPH (also known as Jacob Backofen; c. 1670–1733), rabbi, halakhic authority, and author. Born in Prague, Reischer studied under Aaron Simeon Spira, rabbi of Prague, and was known as a prodigy in his early youth. Afterward he studied under Spira's son, Benjamin Wolf Spira, av bet din of the Prague community and rabbi of Bohemia, whose son-in-law he subsequently became. His brothers-in-law were Elijah Spira and David *Oppenheim. Reischer's surname, borne by his grandfather and uncles (see introduction to his Minḥat Ya'akov), derives from the fact that his family came from Rzeszow, Poland, and not, as has been erroneously stated, because he served as rabbi of that town.
While still young, he became dayyan of the "great bet din of *Prague." He was appointed av bet din of Ansbach, capital of Bavaria, and head of its yeshivah in 1709, and in 1715 av bet din of Worms. There, students flocked to him from all parts of Europe. He had, however, opponents who persecuted him. About 1718, he was appointed av bet din and head of the yeshivah of the important community of Metz. There, too, he did not find peace. He related that in 1728 "malicious men, as hard as iron, who hated me without cause, set upon me with intent to destroy me by a false libel, to have me imprisoned." His first work, Minḥat Ya'akov, was published, while he was still young, in Prague in 1689. In the course of time he was accepted by contemporary rabbis as a final authority (Shevut Ya'akov, vol. 1, no. 28; vol. 3, no. 61), and problems were addressed to him from the whole Diaspora, e.g., Italy, and also from Ereẓ Israel (ibid., vol. 1, nos. 93 and 99). He made a point of defending the *rishonim from the criticism of later writers, and endeavored to justify the Shulḥan Arukh against its critics. But there were also those, particularly among the Sephardi rabbis of Jerusalem, who openly censured his habit of criticizing rishonim and *aḥaronim (ibid., vol. 1, no. 22), and criticized him in their works. His replies to these criticisms were not always couched in moderate language (see Lo Hibbit Aven be-Ya'akov). The main target of his criticism was Joseph b. David of Breslau, author of Ḥok Yosef (Amsterdam, 1730). Jacob's only remaining son, Simeon, av bet din of Danzig, died in 1715.
Reischer was the author of the following works: (1) Minḥat Ya'akov (Prague, 1689) – part 1 is an exposition of the Torat ha-Ḥattat of Moses *Isserles, and part 2, entitled Torat ha-Shelamim, is an exposition of Hilkhot Niddah of the Shulḥan Arukh together with expositions and supplements to the Kunteres ha-Sefekot of *Shabbetai b. Meir ha-Kohen and responsa; a second edition, entitled Solet le-Minḥah ve-Shemen le-Minḥah (Dessau, 1696), contained the glosses of his son, Simeon; (2) Ḥok le-Ya'akov, novellae and expositions on Hilkhot Pesaḥ of the Shulḥan Arukh, subsequently included in the large edition of the Shulḥan Arukh; (3) Shevut Ya'akov, responsa in three parts – part 1 (Halle, 1710) also contains "Pe'er Ya'akov," the residue of his novellae on the Talmud which were destroyed by fire in 1689, part 2 (Offenbach, 1711) contains a revised edition of the laws of migo and sefek sefeka ("double doubt"), which had been published separately in Prague in 1689, and part 3 (Metz, 1789) contains his "Lo Hibbit Aven be-Ya'akov," a reply to the attacks on his first works; (4) Iyyun
A. Cahen, in: REJ, 8 (1884), 271–3; Fuenn, Keneset, 575f.; A. Marx, in: JQR, 8 (1917/18), 271f.; C. Tchernowitz, Toledot ha-Posekim, 3 (1947), 65, 164, 187–90.