Gershom Scholem was a scholar of Jewish mysticism. In one of his books he said that you could study the history of Jewish mystics and the Kabbalah without being religious yourself, and this was his approach. I find it memorable. His numerous books and articles, based on his wide knowledge of history and languages, made an enormous difference in the perception and scholarship of Jewish history and culture. I have read and enjoyed many of them, most famous of which is his long biography Sabbatai Sevi: The Mystical Messiah.
Before Scholem's works were published, scholars were in a weird kind of denial about Jewish mystics, because the scholars themselves were trying to invent a sort of sanitized history of Judaism, making it respectable to the rational 19th century views they themselves held. (Maybe this is an exaggeration, but there's a grain of truth in it. Anyway I find many of those pre-Scholem scholars deadly dull!) He founded the entire field of study of Jewish mystics, and his books are fundamental.
Scholem's autobiography, From Berlin to Jerusalem: Memories of My Youth, tells the really compelling story of how he became a scholar of Jewish mysticism as well as being an early Zionist and one of the founders of the Hebrew University of Jerusalem. As an adolescent, he found life in Germany uncomfortable and untenable because of the anti-Jewish climate throughout the society, especially in academia, and he committed himself to earn a doctorate and then go to Jerusalem. Obviously he wrote after the Holocaust, so he had hindsight, but the foresight that he demonstrated was clearly unusual and penetrating. His friendship with Walter Benjamin was full of contradictions, as Benjamin wasn't as forward-looking.