Read the title, or first page of the Book of Mormon and the book of Doctrine and Covenants and see what they say of Orson Pratt.

Elder Pratt was one of the pioneers, he and Erastus Snow being the first two men of that company to enter Salt Lake Valley.
Another man who came to see Joseph while yet at Fayette was Sidney Rigdon, a former Campbellite preacher whom Parley P.Pratt had baptized at Kirtland.

Elder Rigdon also became a prominent man in the Church, being first counselor to President Joseph Smith during the life time of the prophet.

He took an active part in all the affairs of the Church up to within a few months of the prophet's death.

He was greatly disappointed because he was not chosen to succeed Joseph as the leader of the Church, and soon after apostatized.