Menachem Mendel Schneersohn (Yiddish: מנחם מענדל שניאורסאהן; September 20, 1789 – March 17, 1866) also known as the Tzemach Tzedek (Hebrew: "Righteous Sprout" or "Righteous Scion") was an Orthodox rabbi, leading 19th-century posek, and the third rebbe (spiritual leader) of the Chabad Lubavitch Hasidic movement.

His mother Devorah Leah died three years later, and her father Rabbi Shneur Zalman of Liadi raised him as his own son.

After his father-in-law/uncle's death, and a three-year interregnum during which he tried to persuade the Hasidim to accept his brother-in-law Menachem-Nachum Schneuri or his uncle Chaim-Avraham as their leader,[1] he assumed the leadership of Lubavitch on the eve of Shavuot 5591 (May 5, 1831, OS).

[citation needed] He was known as the Tzemach Tzedek after the title of a voluminous compendium of Halakha (Jewish law) that he authored.

He also authored a philosophical text entitled "Sefer Chakira: Derech Emuna" (Book of Philosophy: The Way of Faith).

In the course of his battle against the Haskalah in Russia, he forged a close alliance with Rabbi Yitzchak of Valozhyn, a major leader of the misnagdim, which led to warmer relations between them and the Hasidim.

[5] His close friendship with Professor J Berstenson, the Czar's court physician, often helped the delicate negotiations relating to the welfare of the community.

[1] He set up an organisation called Hevras Techiyas Hameisim to assist Jewish boy-soldiers who were being recruited and converted to Christianity by the Russian army.

[1][6] Repeated attempts by the authorities to entrap him using informers such as Hershel Hodesh, Benjamin the Apostate and Lipman Feldman failed.

Rabbi Yehuda Leib Schneersohn (Maharil) (1808–1866) settled in Kopys a few months after the death of his father, where he founded the Kopust branch of Chabad.