Joseph Smith Jr. was an American religious leader and the founder of Mormonism and the Latter Day Saint movement. Publishing the Book of Mormon at the age of 24, Smith attracted tens of thousands of followers by the time of his death fourteen years later. The religion he founded is followed to the present day by millions of global adherents and several churches, the largest of which is the Church of Jesus Christ of Latter-day Saints.

Mormonism is the theology and religious tradition of the Latter Day Saint movement of Restorationist Christianity started by Joseph Smith in Western New York in the 1820s and 1830s. As a label, Mormonism has been applied to various aspects of the Latter Day Saint movement, although there has been a recent push from the Church of Jesus Christ of Latter-day Saints to distance themselves from this label. A historian, Sydney E. Ahlstrom, wrote in 1982 that, depending on the context, the term Mormonism could refer to “a sect, a mystery cult, a new religion, a church, a people, a nation, or an American subculture; indeed, at different times and places it is all of these."