History of Mormonism, David Whitmer was born on January 7, 1805, in Harrisburg, Pennsylvania. David Whitmer was one of the three witnesses of the Gold Plates.
David heard about Joseph Smith and the Gold Plates in 1828, and traveled to Palmyra, New York and talked with Oliver Cowdery, who told him that there might be some truth in the matter. David was baptized in 1829, a year before the organization of the Church. During the same month he was baptized, David Whitmer, Oliver Cowdery, and Martin Harris were each shown in a vision by an Angel, the Gold Plates. After the vision, they all wrote and signed their testimony, which is now shown in copies of the Book of Mormon.
After the Church was organized, David was ordained the office of High Priest, and was asked to preside over the Church in Missouri while the Church was trying to establish Zion. Joseph later told David that he would be his successor as Prophet.
When the Kirkland Society Bank failed in 1837, Joseph Smith and Sidney Rigdon were persecuted by creditors and they left to Far West Missouri to avoid arrest. This led up to events like David resigning, W.W. Phelps, John Whitmer, and Oliver Cowdery were excommunicated.
After Joseph Smith was murdered, there was much contention in who would be the next prophet. People remembered what Joseph said about David Whitmer being his successor, and David founded the Church of Christ (Whitmerite). David did not attend nor participated in the church himself, and it was dissolved fairly quickly. David stayed in Richmond Missouri, and did not join the exodus to Utah. Oliver Cowdery sustained Brigham Young as Prophet, Seer, and Revelator of the Church, and Oliver bore his testimony of the Book of Mormon and Joseph Smith. He requested to be readmitted to the Church. He was accepted and re-baptized into the Church.
David Whitmer, after Martin Harris and Oliver Cowdery died, became the most interviewed of the three witnesses. He did not get re-baptized into the Church, and renewed the Church of Christ (Whitmerite) by ordaining his son to be an elder. The Whitmer Church survived until the 1960's.
People question why did David not become Joseph's successor to the church. I think that it was because of David's excommunication from the church.