Rabbi Yisroel Meir HaKohen was one of the greatest figures in modern Jewish history. He was recognized as both an outstanding scholar and an extraordinarily righteous man. His impact on Judaism was phenomenal. It is interesting to note that, despite his great stature, he refused to accept any rabbinical position and supported himself from a small grocery run by his saintly wife in the town of Radin where they lived. Rabbi Yisroel Meir devoted himself to the study and teaching of Torah.
Rabbi Yisroel Meir is perhaps best known for his campaign to teach his fellow Jews about the laws of Lashon Hara (forbidden speech). When he was 35 (1873) he published his first book, Chofetz Chaim, which was devoted to this topic. (The name comes from Tehillim (Psalms) 34, “Who is the man that desires life (chofetz chaim) keep your tongue from evil .” He later published two more books on this subject. As has often happened to Judaisms great leaders, Rabbi Yisroel Meir became known by the name of his book and is known worldwide as the Chofetz Chaim.
The Chofetz Chaim wrote on many subjects and ultimately published over 20 books. Some important ones are Ahavas Chesed (Love of Kindness) on the mitzvah of lending money, Machaneh Yisroel (The Jewish Camp) for Jews serving in non-Jewish armies, and Nidchei Yisroel (The Scattered of Israel) for Jews who moved to places where there were few religious Jews, particularly America. He wrote books about the importance of Torah study and many other important issues.
Probably the most important book he wrote was the Mishna Berurah, a six volume commentary on Shulchan Aruch, Orach Chaim (which deals with the laws of daily life and holidays).
Sources: Great Jewish Leaders