Miller, William, 1782–1849, American sectarian leader, b. Pittsfield, Mass. He was the founder of the sect of Second Adventists, sometimes called Millerites. In 1831, convinced from study of the Bible that the prophecies pointed to the second coming of Christ in 1843, he went about spreading his belief among large audiences. Many prepared for the Day of Judgment, and when the year passed without a fulfillment of Miller's prophecy, a date in 1844 was set. In 1845 Miller and his followers founded the Adventist Church.