Rabbi Israel ben Eliezer, the Baal Shem Tov or Besht, is regarded as the founder of Chasidism. The son of Eliezer and Sarah, who according to tradition had him in their old age, he was born between 1690 and 1700, traditions differing on the year. Many sources give his birthplace as Okopy, near Kamianets-Podilskyi, while the historian Moshe Idel places it rather on the edge of Moldavia.

He first married a woman from Okopy, who died soon afterwards without children, and served as shammash of the town's study hall, as an assistant teacher of young children and, for a time, as a shochet. Later, near Brody, he married Chana, daughter of Ephraim and sister of Rabbi Avraham Gershon of Kitov. The couple lived in the mountains between Kitov and Kosov, where he spent time in seclusion and earned a living digging clay. They had two children, Adel and Tzvi.

At the age of thirty-six, in Tlust, he revealed himself as a baal shem, a healer who used the holy Names. From 1740 he lived in Medzhybizh, in Podolia, where tax records list him until 1760 as a "kabbalist" and later a "baal shem". A circle of disciples formed around him: Rabbi Yaakov Yosef of Polonne, author of Toldot Yaakov Yosef; Rabbi Dov Ber, the Maggid of Mezritch, who succeeded him; Rabbi Pinchas of Korets; the Maggid of Zlotchov; and Rabbi Meir of Premishlan.

His teaching stressed proper intention in prayer and in the performance of mitzvot, the holiness of the letters of sacred texts, and joy, rather than self-mortification, as the path to closeness to God. He wrote no book; his Iggeret Aliyat HaNeshamah survives, and his sayings were collected above all in Keter Shem Tov and Tzavaat HaRivash.

He passed away on Shavuot 5520 (1760), according to the most widely accepted date on the first day of the festival, 6 Sivan (22 May 1760); others give 7 Sivan. He is buried in the old Jewish cemetery of Medzhybizh.