|The Alter Rebbe - Rabbi Shneur Zalman of Liadi author of The Tanya|
The 18th of Kislev marks the completion of the annual cycle of daily readings from the Tanya. The 19th and 20th of Kislev are the "Rosh HaShanah of Chassidus".
On Yud-Tes Kislev we re-commence the annual cycle of daily readings in Tanya, as divided by the Rebbe Rayatz.
It is the anniversary of the release of the Alter Rebbe - Rabbi Shneur Zalman of Liadi [Hebrew: שניאור זלמן מליאדי], the first Rebbe of Chabad, who was informed upon by misnagdim in Russia and arrested on trumped-up charges of supporting the Ottoman Empire.
His informers pointed to the fact that he would urge his followers to send money to the Land of Israel as "evidence" of his alleged insurrectionist aspirations [in fact, the money was sent to support poor Jews]. At the time, the Land of Israel was a part of the Ottoman Empire, which was at war with Russia.
Rabbi Shneur Zalman was charged with treason, and released in the secular year 1798 on the Jewish date of Tuesday, 19 Kislev.
The 53 days of Rabbi Shneur Zalman's imprisonment are said to correspond to the 53 chapters of the first section of the Tanya.
19 Kislev is also considered to mark the day upon which Rabbi Shneur Zalman was conceived, for he was born exactly nine months later, on 18 Elul. [Shemu'os Vesippurim, Refoel Kahn, vol. 1, p. 39]
Rebbetzin Menuchah Rachel born 
On the very day that Rabbi Schneur Zalman of Liadi was liberated from prison, a granddaughter was born to him -- the daugher of his son Rabbi Dovber and his wife Rebbetzin Sheina. The girl was named Menuchah Rachel -- "Menuchah", meaning "tranquility" [Rachel was the name of a daughter of Rabbi Schneur Zalman who died in her youth].
In 1845, Rebbetzin Menuchah Rachel realized her lifelong desire to live in the Holy Land when she and her husband, Rabbi Yaakov Culi Slonim [d. 1857], led a contingent of Chassidim who settled in Hebron. Famed for her wisdom, piety and erudition, she served as the matriarch of the Chassidic community in Hebron until her passing in her 90th year in 1888.
The 19th of Kislev is also the yahrzeit of R. DovBer, the Maggid of Mezritch, who [as successor to the Baal Shem Tov] was the mentor of the second generation of the chassidic movement - from 5521  until his passing on the third day of the week of Parshas Vayeishev, Yud-Tes Kislev, 5533 . His resting place is in Anipoli.
Rabbi Dov Ber was born in Volhynia in 1710, according to the Jewish Encyclopedia, though other sources say his year of birth is unknown. Little is known about him before he became a disciple of the Baal Shem Tov. A Hasidic legend states that, when he was five years old, his family home burst into flames. On hearing his mother weeping, he asked: "Mother, do we have to be so unhappy because we have lost a house?" She replied that she was mourning the family tree, which was destroyed, and had begun with Rabbi Yohanan, the sandal-maker and master in the Talmud. The boy replied: "And what does that matter! I shall get you a new family tree which begins with me!"
How aptly those words described the role he was later to play; for the boy was destined to become the successor to the Baal Shem Tov.