Originally published in Tzvi M. Rabinowicz (ed.), The encyclopedia of Hasidism (1996), pp. 3-4. Son of R. Moses Horowitz, a descendant of R. Isaiah Horowitz, he was born in Orsha in the district of Moghilev. In his youth, Aaron became a disciple of R. Shneur Zalman of Liady, and he stated that he sat at R….