There is an interesting story in the Deseret News about Joseph Smith - founder of the Church of Latter Saints (often called the Mormon Church) Here's a sentence from the article:
"Historians and critics have struggled for more than a century to identify children Joseph Smith may have had through polygamous marriages in the 1840s. If definitive answers could be found, it would shed light on how plural marriage was introduced to Mormons by Joseph Smith in Illinois. Brigham Young succeeded Joseph Smith as leader of the LDS Church and announced the practice publicly in Utah. The church ended polygamy in 1890."
The researcher. Ugo Perego, is a solid member of the genetic genealogical community. His work - as reported in the article - is the sort of research that we all aspire to do with our dna testing - to explore and either prove or disprove a historic legend. Based on what he found, there is still no evidence that Joseph Smith was a polygamist.
So - was Brigham Young the man who introduced Polygamy to the LDS? I guess we'll have to wait for the answer