What role did Brigham Young play in the Mormon Church?

Brigham Young was one of the first Apostles ordained in the Church of Jesus Christ of Latter-day Saints (the "Mormon" church) in 1835. He was a friend to the Prophet Joseph Smith. When Joseph Smith was murdered, Brigham Young carried out Joseph's prophecy and lead the Mormons across the country to safety in the Rocky Mountains. There he was appointed as the second President of the Church. Brigham Young was the President of the Church from 1847 until his death in 1877, making him (by far) the longest serving President in the history of the Church. Because of his long years of leadership in the early years of the Church, as well as his organization and settlement of the Utah Territory, he has become very influential and well-known.