Oliver H. P. Cowdery (October 3, 1806 – March 3, 1850) was an American religious leader who, with Joseph Smith, was an important participant in the formative period of the Latter Day Saint movement in the 1820s and 1830s.

He was the principal scribe to the Book of Mormon, the first baptized Latter Day Saint, one of the Three Witnesses to the Book of Mormon's golden plates, one of the first Latter Day Saint apostles, a key early missionary, and a member of the First Presidency in Kirtland.

Cowdery's relationship with Joseph Smith and the church's leadership deteriorated in the mid-1830s, and in 1838 he was excommunicated with several other prominent Missouri leaders amid a leadership struggle with Smith.

After his excommunication, Cowdery moved to Wisconsin, where he practiced law and became involved in local politics. Cowdery briefly joined a Methodist church before being rebaptized into the Church of Jesus Christ of Latter-day Saints (LDS Church) in 1848.

Oliver Cowdery was born October 3, 1806, in Wells, Vermont; his father, William, moved the family to the nearby town of Poultney when Cowdery was three years old. His mother, Rebecca Fuller Cowdery, died on September 3, 1809.

At age 20, Cowdery left Vermont for upstate New York, where his older brothers had settled. He clerked at a store for just over two years and in 1829 became a school teacher in Manchester. Cowdery lodged with different families in the area, including that of Joseph Smith, Sr., who was said to have provided Cowdery with additional information about the golden plates of which Cowdery said he had heard "from all quarters."

Cowdery met Joseph Smith on April 5, 1829—a year and a day before the official founding of the Church of Christ—and heard from him how he had received golden plates containing ancient writings. Cowdery told Smith that he had seen the golden plates in a vision before the two had met. Before meeting Cowdery, Smith had virtually stopped translating after the first 116 pages had been lost by Martin Harris. Working with Cowdery, however, Smith completed the manuscript of what would become the Book of Mormon between April 7 and June 1829, in what Richard Bushman later called a "burst of rapid-fire translation." Cowdery also unsuccessfully attempted to translate part of the Book of Mormon by himself.

Cowdery and Smith reported that on May 15, 1829, they received the Aaronic priesthood from the resurrected John the Baptist, after which they baptized each other in the Susquehanna River. Cowdery said that he and Smith later went into the forest and prayed "until a glorious light encircled us, and as we arose on account of the light, three persons stood before us dressed in white, their faces beaming with glory." One of the three announced that he was the Apostle Peter and said the others were the apostles James and John, who many presume then gave them the Melchizedek priesthood.