Rabbi Nachman of Breslov
The great-grandson of the Baal Shem Tov, Rabbi Nachman of Breslov (sometimes called Bratzlav, Breslau or Bratislava) was one of the most creative, influential and profound of the Chassidic masters and the founder of the Breslover Chasidic sect. Breslov is a town in the Ukraine where Rabbi Nachman spent the end of his life, but some say the name Breslov comes from the Hebrew bris lev, meaning "covenant of the heart."
From his youth, he followed a path of asceticism and prayer, though he warned his followers not to abuse themselves physically. He emphasized living life with joy and happiness. One of his best-known sayings is, "It is a great mitzvah to be happy."
He was a passionate individual, given to intense swings of emotions. These he put toward the service of G-d, and spoke often of how to find G-d even in the low states of mind, and how to serve Him during the emotional highs.
Central to his teachings is the role of the tzaddik, who has the power to descend into the darkness to redeem lost souls; the path of prayer as the main expression of religious life. His main work is Likutey Moharan, composed partly by himself, partly by his chief disciple, Rabbi Nossan Sternhartz. The book is a collection of sermons delivered by Rabbi Nachman, given mostly on the holidays when his Chassidim gathered. The lessons are long and complex, masterfully drawing on the entire body of Talmud, Midrashic and Kabbalistic literature. Ideas are connected by a poetic and intuitive grasp of the texts. In addition, Rabbi Nachman wrote thirteen Tales — mythical stories of kings and wizards based upon Kabbalistic thought and capturing the essence of Rabbi Nachmans teachings. These tales were known to have influenced later authors such as Franz Kafka.
Rabbi Nachman died of Tuberculoses at the age of 38. Despite the fact that there was never another Breslov Rebbe to fill his place, the mystery and depth of his teachings continue to attract students today, and Breslover Chassidism is one of the largest and most vibrant of Chassidic groups.
Sources: Orthodox Union; Judaism 101