Rabbi Levi Yitzchok Schneerson was the grandson of the Tzemach Tzedek, the third Lubavitcher Rebbe, and a sixth-generation descendant of the founder of the Chabad-Lubavitch movement, Rabbi Shneur Zalman of Liadi (known as the Alter Rebbe.) His eldest son, Rabbi Menachem Mendel Schneerson, who later became the present Lubavitcher Rebbe, married the daughter of Rabbi Yosef Yitzchok Schneerson, the sixth Lubavitcher Rebbe (known as the Rebbe Rayatz).
Rabbi Levi Yitzchok was an extremely devoted chassid of Rabbi Sholom Dovber Schneerson, the fifth Lubavitcher Rebbe (also known as the Rebbe Rashab.) The Rebbe Rashab recognized Rabbi Levi Yitzchok’s potential when he was still very young and began to entrust him with certain important tasks at the tender age of eighteen, including various missions abroad. He is particularly remembered for his work with the Jewish soldiers who were sent to fight in the Russo-Japanese war in 1905. He also played a key role in assisting Mendel Beilis, the defendant in the infamous blood libel case that took place in Kiev in 1912.
After the Rebbe Rashab passed away, Rabbi Levi Yitzchok became equally dedicated to his successor, the Rebbe Rayatz.