Theodore Parker, 1810-1860, was a controversial Unitarian minister and member of the Transcendental Club. As his religious beliefs changed, Parker became increasingly at odds with Unitarianism, and, in 1846, he became minister to the 28th Congregational Society, a Boston church that initially met at the Melodeon Theater and later at the Boston Music Hall. There, he drew as many as 2,000 people to his services.
Parker was a latecomer to abolitionism. However, he vehemently opposed the expansion of slavery and was an active opponent of the Fugitive Slave Law. After the raid on Harpers Ferry, he publicly defended John Brown's actions. By then Parker was seriously ill with tuberculosis, the disease that had killed his parents and most of his siblings while he was still young, and he died abroad in 1860.
Further Reading:
Commager, Henry Steele. Theodore Parker. Boston: Little, Brown, and Company, 1936.
Grodzins, Dean. American Heretic: Theodore Parker and Transcendentalism. Chapel Hill: University of North Carolina Press, 2002.