Amasa Mason Lyman (1813-1877) was a Mormon polygamist and early prominent leader in The Church of Jesus Christ of Latter-day Saints who served multiple missions throughout the United States. Later in life, he preached false doctrine while serving as mission president in Europe and was subsequently excommunicated.

Lyman was born in March of 1813 in Lyman, Grafton, New Hampshire. He was introduced to the LDS church by Orsan Pratt and Lyman E. Johnson and chose to be baptized on April 27, 1832. He served missions in many states, including Ohio, Virginia, New York, Missouri, Pennsylvania, Iowa, Illinois, Indiana, and California. He was ordained a seventy in 1835, ordained an apostle in the Quorum of the Twelve in 1842, and served as a counselor in the First Presidency from 1843 to 1844. In 1847, he traveled to Utah with the Brigham Young Company. During his lifetime, he had nine wives.

In March 1862, he delivered a sermon in Dundee, Scotland in which he denied the atonement of Jesus Christ. After being deprived of apostleship in 1867, he was repentant and formally asked forgiveness of his error, but later, he continued to preach this false doctrine and was excommunicated in 1870. He then became president of the Godbeite Church of Zion. He died in February of 1877 in Millard County, Utah.