Jewish mystic, fervent Zionist, and first chief rabbi of Palestine under the League of Nations mandate to Great Britain to administer Palestine.

After serving as rabbi in a number of small towns in eastern Europe, in 1904 Kook became rabbi of the seaport city of Jaffa in Palestine, and he established a yeshiva, or Jewish academy, there. During World War I, Kook, who had left Palestine for a visit to Germany, was interned as an alien, but he escaped to England via Switzerland. He became rabbi of the congregation Machzike Hadath in London, where he aroused popular support for the Balfour Declaration (1917), which furnished the basis for the League of Nations Palestinian mandate. After the war, in 1919, Kook was appointed rabbi of the Ashkenazic (German and Polish) communities in Jerusalem and in 1921 was elected chief rabbi of Palestine, a post he held for the rest of his life.

According to Kook's philosophy of repentance, man's separation from God is not an objective fact but a consequence of human “forgetfulness” of a higher existence. Thus repentance, to be achieved through Torah, can restore man's unity with the divine.

A mystic by nature, Kook viewed Jewish national revival as part of the divine plan for strengthening faith against the rising tide of heresy. He expounded this philosophy in several cryptic essays, many of which were published posthumously under the title Orot ha-qodesh, 3 vol. (1963–64; “Lights of Holiness”).

Other important works are Iggerot ha Reʾayah (1962–65; “Letters” 【Reʾayah is a play on the letters of his name and the Hebrew word for “vision”】); Orot (1961; “Lights”); Orot ha-Teshuvah (1955; Rabbi Kook's Philosophy of Repentance, 1968); Eretz Hefetz (1930; “Precious Land”); Eder ha-Yekar ve-Ikvei ha-ton (1967; “The Precious Mantle and Footsteps of the Flock”); and (among a number of Halakhic writings) Shabbat ha-Areẓ (1937) and Mishpat Kohen (1966).