Brigham Young was an early Mormon leader. He is often known as the "American Moses" for leading a group of persecuted Mormon settlers on an exodus through the desert to Utah, the "Promised Land". As the leader of the church he was believed to be guided by the Hand of God and to speak with the voice of the Prophet, and held nearly complete control over the Mormon territories. He features as a secondary antagonist in A Study in Scarlet, where his actions with regard to the marriage of Lucy Ferrier are the catalyst for the story.
After the murder of the Prophet Joseph Smith in 1844, Brigham Young became leader of the Mormon church. As persecution of the church continued to increase, in 1847 Young announced that he had received a revelation from God, who commanded him to lead his people west into Zion, the Promised Land. Gathering a group of settlers numbering over ten thousand, he led his flock deep into the arid lands of the western United States to found a new country of the Elect.
As the group passed the Sierra Blanco, they stumbled upon two starving and dehydrated people, the only survivors of a doomed wagon party: John Ferrier and Lucy, a young girl whom Ferrier adopted after the recent death of her mother. The pioneers questioned Ferrier, asking him who he was, and revealing that they were the Mormons, seeking refuge from the violent and godless. The pioneers brought the two before Young, who, after hearing their story, agreed to rescue the Ferriers in exchange for their conversion to Mormonism. With Ferrier's acquiescence, Young entrusted the two to Elder Stangerson's care for food and instruction in the Mormon faith.
Eventually the immigrants reached the Salt Lake Valley, which Young proclaimed to be the Promised Land. He proved himself an capable administrator, drawing up charts for the future Salt Lake City, including the construction of a new Temple, and parceling out farmland to his disciples. Ferrier, having during their journey become very well-respected by the Mormon Elders, was given one of the best farms, and over time grew to be very rich, second only to Young and the other Mormon Elders.
However, over time Ferrier's apparent indifference towards his adopted religion began to create tensions with the Elders. These tensions boiled over years later when Lucy came of marrying age and fell in love with Jefferson Hope, a non-Mormon. Young personally paid Ferrier a visit at his home. After questioning Ferrier's devotion to the church, a point illustrated by his refusal to marry, Young revealed the true reason for his visit: he was outraged that Ferrier had given Lucy permission to marry a gentile, a grievous sin in the eyes of the church. In order to prove his faith, Young demanded that he instead make her marry the son of either Elders Stangerson or Drebber. When Ferrier balked, Young angrily told him she would have a month to decide before turning to leave. On his way out of the house, he paused at the door to threaten Ferrier that he would wish had died on the Sierra should he try and fight the wishes of the Mormon Elders.
When Ferrier continued to resist the elders, Young sent the Danites after him to first threaten him into compliance and then recover him and Lucy.