Yisrael Meir Kagan
In 1869, Rabbi Kagan opened up a yeshiva in Radun, Belarus that became known as the Radin Yeshiva, and was sometimes also called "Yeshivas Chofetz Chaim", since Rabbi Kagan, who opened it, was called "the Chofetz Chaim". In the 1870s, he wrote the Sefer Chofetz Chaim, a book that discusses the halachos (Jewish laws) about not saying hurtful things. The book was very popular, and nowadays, he's known as the "Chofetz Chaim." In 1907, he completed a six volume series called the Mishna Berurah, in which he discussed the halachos pertaining to Jews' everyday life, Shabbat, and holidays. He became famous to Orthodox Jews and many people came to visit him for blessings; he was considered the leader of Orthodox Jewry. He died on September 15, 1933.