William Miller (1782–1849), a lay Bible student (later a Baptist preacher), predicted that Christ would return to earth some time between 21 March 1843 and 21 March 1844. One of Miller’s followers postponed the date to 22 October 1844. When Christ did not return on that day, however, there was ‘great disappointment’.
Anthony Hoekema, “Seventh-Day Adventism,” in Sinclair B. Ferguson and J.I. Packer ed. New Dictionary of Theology (Downers Grove, IL: InterVarsity Press, 2000), 637.