Joseph Smith (the founder of mormonism was married to over 30 women, including women who were still married to living husbands (by the way, it is called polyandry, when a women is married to multiple men):
“Now if any of you will deny the plurality of wives, and continue to do so, I promise that you will be damned,” (Journal of Discourses, vol. 3, p. 266).
“The only men who become Gods, even the Sons of God, are those who enter into polygamy,” (Journal of Discourses, vol. 11, p. 269).
In 1869 Wilford Woodruff, Mormonism’s future fourth president, taught:
“If we were to do away with polygamy, it would only be one feather in the bird, one ordinance in the Church and kingdom. Do away with that, then we must do away with prophets and Apostles, with revelation and the gifts and graces of the Gospel, and finally give up our religion altogether and turn sectarians and do as the world does, then all would be right. We just can’t do that, for God has commanded us to build up His kingdom and to bear our testimony to the nations of the earth, and we are going to do it, come life or come death. He has told us to do thus, and we shall obey Him in days to come as we have in days past” (Journal of Discourses 13:165 – p.166).
Even as late as 1879, Joseph F. Smith was insisting that plural marriage was essential for LDS exaltation. Speaking at the funeral of William Clayton, Mormonism’s future sixth president, stated:
“This doctrine of eternal union of husband and wife, and of plural marriage, is one of the most important doctrines ever revealed to man in any age of the world. Without it man would come to a full stop; without it we never could be exalted to associate with and become god…” (Journal of Discourses 21:9).
If you don’t think these quotes are accurate, you can look them up for your self on the BYU website (BYU is the Mormon church’s officially sponsored institution), where they cite the Journal of Discourses as scripture:
“Inasmuch as laws have been enacted by Congress forbidding plural marriages, which laws have been pronounced constitutional by the court of last resort, I hereby declare my intention to submit to those laws, and to use my influence with the members of the Church over which I preside to have them do likewise.“Willford Woodruff, Official Declaration ( http://www.lds.org/
scriptures/dc-testament/od/1? lang=eng )
“Obviously the holy practice [of polygamy] will commence again after the Second Coming of the Son of Man and the ushering in of the millennium.”
Bruce R. McConkie, in the book Mormon Doctrine