Martha McBride Knight Smith Kimball (March 17, 1805 – November 20, 1901) was a founding member of the Relief Society of the Church of Jesus Christ of Latter Day Saints, which was organized on her birthday in 1842. She was married to early Latter Day Saint leader Vinson Knight, by whom she had seven children. In 1842 she was sealed as a plural wife to Joseph Smith. In January 1846, she was married polygamously to Heber C. Kimball, by whom she had one child, a son, who was born at Winter Quarters and died there as an infant. She later emigrated to Utah Territory, where she resided in various locations across the territory until her death at age 96. She was a witness to, and in some instances a key participant in, some of the pivotal events in early Latter Day Saint history.