Joseph Smith, founder of Mormonism, was the first Mormon prophet to practice polygamy.

Source at Mormon Handbook Polygamy Joseph Smith, founder of Mormonism, was the first Mormon prophet to practice polygamy. He took as many as 48 wives. Sources: [Official LDS website: FamilySearch.org] [A comprehensive PDF] [Wikipedia] Many were teenagers, as young as 13 years old. Many were already married to other men and continued in polyandry: having more than one husband. He married pairs of sisters, and even took a mother and her daughter for wives. The wives of the prophets Joseph F. Smith's family Six wives & 48 children The first seven Mormon prophets had at least 135 wives. Mormon prophet Number of wives Joseph Smith 48 Brigham Young 55 John Taylor 7 Wilford Woodruff 5 Lorenzo Snow 11 Joseph F. Smith 6 Heber J. Grant 3 Summary of Events From 1830 to 1876, LDS scripture was consistent in prohibited polygamy: Book of Mormon: Jacob, chapter 2; Doctrine and Covenants, Section 101 (removed in 1876). During this time the church publicly taught against polygamy and denied practicing it, while church authorities were privately taking plural wives. In 1852 Brigham Young, the second Mormon prophet, publicly admitted the practice of polygamy. In 1876, Section 132 of the Doctrine and Covenants, which allows polygamy, was added to the Doctrine and Covenants. Section 101 which condemns it was removed. Section 132 remains part of the LDS canon today. Under pressure from the federal government to end polygamy, which passed law to disincorporate the church and seize its assets, Wilford Woodruff, the fourth Mormon prophet, announced he had received a "revelation" to officially end the practice. This announcement is knows as the 1890 Manifesto or Official Declaration—1. 14 years later, congressional hearings uncover church authorities still taking plural wives in secret, in disregard to the 1890 revelation. In response, Joseph F. Smith, the sixth Mormon prophet, issued what is known as the "Second Manifesto" condemning polygamy. As late as 1943 it was uncovered that Mormon apostle Richard Lyman was secretly practicing polygamy.