Rabbi Kalonymus Kalman HaLevi Epstein, known as the Maor VaShemesh after his work, was born in 1751 in Nowy Korczyn (Neustadt), Poland, the son of Aharon, into a very poor family of ten children that moved to Kraków when he was five. As a child he sold rolls baked by his parents and then slipped into the beit midrash to hear the sermons of the city's scholars. One day a wealthy man jokingly asked him to repeat the sermon he had just heard: he did so word for word, and the man paid for his studies and made him his son-in-law.

Shortly after his marriage he met Rabbi Elimelech of Lizhensk during the latter's visit to Kraków, followed him to Lizhensk and, despite his youth, became one of his leading disciples. In 1785, on his teacher's instruction, he returned to Kraków to spread Chassidism. He met fierce opposition: the city's rabbinical court even banned him, on pain of cherem, from spreading his teaching. Over time the opposition subsided and his reputation as a tzaddik and kabbalist grew. After Rabbi Elimelech's death he regarded himself as a disciple of the Seer of Lublin, Rabbi Menachem Mendel of Rymanov and the Maggid of Kozhnitz.

His Torah commentary, Maor VaShemesh, is one of the great classics of Chassidic literature, recording many teachings of his masters. He passed away in Kraków on 1 Tammuz 5583 (1823) and rests in the city's new Jewish cemetery; at his request, no ohel was built over his grave.