The third Lubavitcher Rebbe, Rabbi Menachem Mendel , was the son-in-law of the Mitteler Rebbe and the grandson of the Alter Rebbe. His erudition was extraordinary even for a Rebbe, and he introduced a number of new and particularly sublime ideas into Chabad philosophy. He is known as the "Rebbe Tzemach Tzedek" after the opening words of his magnum opus. Significantly, Tzemach is one of the traditional Jewish names for Moshiach.
The Tzemach Tzedek was incredibly knowledgeable in Chassidus, Nigleh, Kabbalah, and Halachah. His book Derech Mitzvosecha is an analysis, from the Chassidishe viewpoint, of all the various approaches to and interpretations of the fundamental ideas of the Torah. However his fame, like that of his predecessors, was based not only on his erudition, but also on his practical efforts on the behalf of the Jewish people. In addition to numerous educational institutions, he established agricultural settlements where impoverished and starving families could find a steady and honorable livelihood.
During the time of the Tzemach Tzedek, the so-called maskilim, the adherents of the Haskalah (Enlightenment movement), whose goal was to introduce the Jews to "world culture," attempted to reform the traditional system of Jewish education. They sought to introduce secular subjects, taught from an atheistic viewpoint, to the curricula of Jewish schools. The Tzemach Tzedek spearheaded the struggle against these endeavors, with their inherent danger of mass assimilation. He succeeded in rallying the support of all the opponents to the reform, including some prominent rabbis from among the misnagdim. The efforts of the Tzemach Tzedek won him enormous popularity in every sector of Torah-observant Jewry. As a result, even the czarist authorities were forced to recognize his special status, awarding him the title of "honorary citizen of the Russian Empire." All the subsequent Lubavitcher Rebbeim inherited this title.
Another heroic act of the Tzemach Tzedek was the rescue of thousands of Jewish children from the perils of forced conversion and even death. In 1827, Czar Nicholas I issued the infamous conscription decree, under which all Jewish boys twelve years of age and older could be drafted into the army. Responsibility for enforcing this decree was placed on Jewish communities, which were required to fill a conscription quota of ten boys for every thousand Jewish residents. Even though a similar law was issued for gentiles, the quotas were lower, and it provided for various privileges and exemptions.
When it was discovered that most of the Jewish communities were trying to evade this brutal decree, the government dispatched secret agents to towns and villages to hunt down the draft dodgers. Thousands of small boys some of them barely seven years old - were seized and forcibly sent to orphanages or peasant families, where they would be kept until the age of twelve. At that point, they were sent off to military barracks. At the age of eighteen, they would embark on twenty-five years of regular military duty. The majority of these boys never made it back to their families. As a rule, children's freedom could be bought by bribing the czarist "snatchers," but the families were so desperately poor that this avenue of escape was out of the question. The conscription decree caused deep dismay among Russian Jewry; people vainly looked for ways to save their children. The Tzemach Tzedek founded a clandestine society known as "those who raise the dead" for the rescue of kidnapped children. They monitored all that was happening to the conscripted children, raised money, bribed czarist officials to issue falsified death certificates, and when the time was right, ransomed the boys. In this way, thousands of stolen children were saved.
The Rebbe Tzemach Tzedek was nistalek in the year 5626 in Lubavitch and his holy resting place is in Lubavitch.