Oliver Cowdery (3 October 1806 - 3 March 1850) was the primary participant with Joseph Smith, Jr in the early formative period of Mormonism from 1829 through 1836. Mormons esteem Cowdery as an exemplary christian and a man of honor.
An acquaintance of Joseph Smith, Jr's father, Joseph Smith, Sr, Cowdery met Joseph Smith on April 5, 1829, after learning from his family that the younger Smith had purportedly received Golden Plates containing ancient Native American writings. See Joseph Smith--History 1:66. From April 7 to June 1829, Cowdery acted as Smith's scribe for the purported translation of the plates into what would later become The Book of Mormon. Cowdery also purportedly attempted to translate part of The Book of Mormon, but was unsuccessful. See History of the Church 1:36-38.
During the purported translation of the Golden Plates, Cowdery and Smith said they were present together on May 15, 1829 and a second time that month, when angels gave them priesthood authority. See History of the Church 1:39-42. Also in 1829, Cowdery received a revelation entitled "Articles of the Church of Christ", which directed the formation of the Church of Christ (later renamed the Church of Jesus Christ of Latter-day Saints). When the Church was later formed on April 6, 1830, Cowdery was designated the "second elder" after Joseph Smith. He was second in authority to Smith in the Church of Christ from its organization through 1836. He helped Smith revise and publish Smith's revelations for the Doctrine and Covenants in 1835.
From 1838 to 1848, Cowdery was estranged from Smith and the church by his own choice due to his "belief on the outward government of this Church" (Far West Record, pp. 165-66) and by excommunication for inactivity, accusing the Prophet of adultery, and three charges of beginning law practice and seeking to collect debts after the Kirtland bank failure (according to the Church court).
In 1848, after Smith's death, Cowdery humbly joined the Church of Jesus Christ of Latter-day Saints again in Winter Quarters, Nebraska.
On March 3, 1850 Cowdery died in Richmond, Missouri of a respiratory illness.