Yehuda Ashlag (1885–1954) or Yehuda Leib Ha-Levi Ashlag (Hebrew: יְהוּדָה לֵיבּ הַלֵּוִי אַשְׁלַג), also known as the Baal Ha-Sulam (בַּעַל הַסּוּלָם, "Author of The Ladder") in reference to his magnum opus, was an Orthodox rabbi, kabbalist, social justice universalist, and altruistic communist born in Łuków, Congress Poland, Russian Empire, to a family of scholars connected to the Hasidic courts of Porisov and Belz. Rabbi Ashlag lived in the Holy Land from 1922 until his death in 1954 (except for two years in England). In addition to his Sulam commentary on the Zohar, his other primary work, Talmud Eser Sefirot is regarded as the central textbook for students of Kabbalah. Ashlag systematically interpreted the wisdom and promoted its wide dissemination. In line with his directives, many contemporary adherents of Ashlag's teachings strive to spread Kabbalah to the masses.

Ashlag reputedly studied Kabbalah from the age of seven, hiding pages from the book Etz Chaim "The Tree of Life" by Rabbi Hayyim ben Joseph Vital in the Talmudic tractate he was meant to be studying. At the age of twelve, he studied the Talmud independently. By nineteen, Ashlag's knowledge of the Torah was profound enough for the rabbis of Warsaw to confer upon him the title of rabbi.

During this period he worked as a judge in the court of the Warsaw rabbis and also gained experience as a teacher for training judges for Jewish courts. Ashlag also studied German while in Warsaw, read original texts of Georg Wilhelm Friedrich Hegel, Karl Marx, Friedrich Nietzsche, and Arthur Schopenhauer, and took part in socialist and communist demonstrations.

While still in Poland, he met an unidentified Warsaw merchant, who revealed himself to Ashlag as a Kabbalist. Ashlag studied with this particular teacher every night for three months, he said, “until my arrogance separated us,” and the teacher disappeared. A few months later Ashlag met the teacher again, and after pleading with him, convinced him to reveal an important kabbalistic secret. The next day, the teacher died.

In 1921, at the age of 36, Ashlag made the decision to emigrate to the Land of Israel or Palestine at the time, a journey that took several months. He spent the first few years living anonymously, supporting his family through manual labor by day and writing his commentaries at night. Eventually, he was recognized through his work, and was appointed Rabbi of Givat Shaul, Jerusalem in 1924.

Ashlag was friendly with the Kabbalist and Chief Rabbi of Mandatory Palestine, Abraham Isaac Kook, who recognized Ashlag as a great follower of Isaac Luria. Ashlag had high hopes of meeting great Kabbalists in Jerusalem including the Sephardi followers of the great 18th-century Yemeni Jewish Kabbalist Shalom Sharabi. However, he was profoundly disappointed by his encounter with them. Their views about Kabbalah ran contrary to Ashlag's experience with the teaching as a means of profound personal transformation and spiritual illumination, by becoming a vessel for divine light.

In 1926 Ashlag left for London, and it was there that he wrote his commentary on The Arizal's (Isaac Luria) book Etz Chaim. This work is entitled Panim Meirot wMasbirot. It took him one and a half years to complete this work. It was published in 1927, and in 1928 Ashlag returned to the Land of Israel (Mandatory Palestine).

In 1932 Ashlag and his family moved to Jaffa. During this period, Ashlag also began one of his main works, Talmud Eser Sefirot, a commentary on all the writings of Isaac Luria. In this undertaking, he developed a comprehensive explanation of the sequence of the creation of all of the upper worlds (Olamot Elyonim), starting with the source of emanation (Ma'atzil) and finishing with our world (Olam HaZeh). The work is divided into six volumes, containing sixteen parts and over two thousand pages. Some today consider it as the core of the entire teaching of Kabbalah.