Leibovich (Leibowitz) Ieshayagu (Ieshayahu, Isaiah) (1903, Riga – 1994, Jerusalem) — biochemist, publicist, public figure.

Ieshayagu Leibovich graduated from the Universities of Berlin and Basel. Doctor of Philosophy (1924, University of Berlin), Doctor of Medicine (1934, University of Basel), Professor of Biochemistry (1942). In 1935, he moved to Palestine. From 1935 to 1994, he taught at the Hebrew University of Jerusalem.

He authored works on organic chemistry, biochemistry, neurophysiology, as well as Judaica (Torah and Commandments in Our Time, 1954; Maimonides’ Faith, 1980, and others), political science (Judaism, the Jewish People and the State of Israel, 1975, and others), philosophy (Body and Soul: The Psychophysical Problem, 1975), and other humanities.

He served as literary editor of the Hebrew Encyclopedia for the natural sciences (vols. 1–21) and later as its editor-in-chief (vols. 10–21).

The concept of Jewish identity developed by Leibovich asserted that Jewish distinctiveness was preserved solely due to a lifestyle based on the practical observance of Halakhic commandments regulating the religious, family, and civil life of Jews. He viewed the voluntary acceptance of the commandments and prohibitions of Judaism as the highest of achievements, surpassing any accomplishment in science, culture, or social justice.

He denied that Zionism had religious or historical roots, interpreting it merely as a natural desire to free oneself from the rule of non-Jews, rather than a path to preserving the continuity of Jewish history. He was a fierce critic of Israeli values and national policy. His statements about the “Judeo-Nazi mentality” of soldiers after the 1982 Lebanon War provoked wide public debate in Israel.

In 1983, a group of scholars published Denial for the Sake of Denial, a volume critically analysing Leibovich’s views. In 1993, he refused the Israel Prize after its nomination ignited fierce public controversy.

His wife was Greta; they had six children. One of their sons, Elia, was head of the Department of Astrophysics at Tel Aviv University and the longest-serving director of the Wise Observatory; their son Uri was a professor of medicine at the Hadassah University Medical Centre; their daughter Iska served as a district prosecutor. His sister Nehama was a world-renowned biblical scholar.