Rabbi Meir Yechiel HaLevi Holtzstock, the Ostrovtser Rebbe, is known as "the tzaddik who fasted for forty years". He was born around 1851 in Sawin, Poland, the son of Avraham Yitzchak, a very poor baker and Chassid of Rabbi Yerachmiel of Peshischa, of the Saraf of Mogielnica, after whom he was named, and of Rabbi Elimelech of Grodzhisk. As a child he watched his father rise at dawn to bake and was inspired to rise too and study.

At ten his father took him to Rabbi Elimelech of Grodzhisk. Once, not daring because of his age to speak up about a question that had gone unanswered, he wrote the solution at night on the door of the beit midrash; when they recognised his childish handwriting, they understood he was a prodigy. He later studied under Rabbi Yisrael Yehoshua of Kutno and at seventeen married the daughter of Rabbi Avraham of Vorka. It is told that he once shut himself in his room after Purim and had finished the entire Talmud by the eve of Pesach.

At twenty-eight he was elected rabbi of Sakranovitz; asked to grant him semicha, the Kutner Rav wrote: "How can a fly with clipped wings testify about an eagle soaring in the sky?" He later became Rebbe in Ostrovtse (Ostrowiec). For the last forty years of his life he fasted every day, eating only a little at night except on Shabbat and festivals, while studying without pause. A great Talmudist and kabbalist, he was famous for teachings that combined pilpul and gematria.

He passed away on 19 Adar 5688 (1928).