R. Aaron ben Moses Ha-Levi Horwitz of Sta-Rosielce (1766–1828), leader of a dissenting group in the Habad branch of Lithuanian Hasidism. Born in Orshva Aaron was a descendant of the family of R. Isaiah Leib Horwitz (Shelah; 1555–1630) and was considered both a brilliant interpreter of hasidic teachings and a prominent mystical innovator. He was the most prominent disciple of R. Shneur Zalman of Lyady, founder of Habad Hasidism (1745–1813), with whom he remained close friends for 30 years between 1783 and 1813. Personal and subsequently ideological disputes estranged him from R. Shneur Zalman's elder son and successor R. Dov Ber (1773–1827), who assumed Habad leadership in a period of ensuing conflict. After R. Shneur Zalman's death in 1813, Aaron headed a major trend of Habad which was marked and differentiated from the mainstream movement in questions concerning spiritual authority and ecstatic religious expression in prayer. While the importance of the intellectual approach to religious worship (hitbonenut in Chabad vocabulary) was accepted by all the followers of R. Shneur Zalman, the role of mystical rapture and the ecstatic-emotional approach, referring to communion with God known and as devekut or hitpa'alut, was intensely disputed. R. Dov Ber maintained a distinction between proper and improper states of ecstasy and stages of mystical rapture, claiming that his perception expressed his father's position. R. Aaron maintained, on the contrary, that he was the true follower of R. Shneur Zalman, who favored unrestricted exaltation in meditation and emotional prayer, which he considered conducive to love and reverence of God, a position which R. Dov Ber refused to accept. The debate is argued forcefully in the books of R. Aaron detailed below and the two tracts by R. Dov Ber – Kuntres ha-Hitpa'alut ("Tract on Ecstasy") and Kuntres ha-Hitbonenut ("Tract on Contemplation"). Aaron's most important works are (1) Sha'arei ha-Yihud ve-ha-Emunah (Shklov, 1820), a commentary completing the second (unfinished) part of the Tanya, the main work of R. Shneur Zalman; (2) Sha'arei ha-Avodah (Shklov, 1821) with a forward known as petah hateshuvah, explaining and defending his approach, considered the true path set by R. Shneur Zalman; (3) Avodat ha-Levi, a compendium of sermons, letters, and miscellaneous works, published posthumously in 1842 in three volumes (Lemberg ed. and in 1866, Warsaw ed.). The composition of some of the most beautiful Habad melodies is attributed to him. Although one of R. Aaron's sons attempted to continue his spiritual leadership in his court after his father death, most of his disciples left him to join the main Habad movement led by R. Menahem Mendel of Lubavitch or other hasidic groups.