As the Prophet and founder of the Mormon Church he was the leader of many thousands of believers. He led them in a desperate search for a safe haven for the community to settle. He built the first temple and drwe thousands of followers to the new religion: Mormonism.
Smith would not lead his Mormons West as he thought it unfit to build the Zion for the coming of Jesus.
Smith was shot dead in 1844 as he tried to escape from jail.
Brigham Young was the new leader of the Mormons and chose to lead them West, to Great Salt Lake where they settled successfully. This was an important turning point for the Mormons.