The Ba'al Shem TovYisroel Baal Shem Tov was the founder of the Chassidic movement. He was born around 1700 and lived for 36 years lived an austere and pious life in relative seclusion without revealing who he was. When he did reveal himself, he won the hearts of the simple people as well as those of some of the greatest scholars of the day who then became his dicsciples.
He opposed ascetic practices and self castigation. His approach was to spread joy and to gently turn the heart towards Hashem. He travelled constantly, spreading his message of prayer, joy and humility.
His successor was R' Dov Ber of Mezeritch.