David Hyrum Smith (November 17, 1844 – August 29, 1904) was an American religious leader, poet, painter, singer, philosopher, and naturalist.

The youngest son of Joseph Smith and Emma Hale Smith, he was an influential missionary and leader in the Reorganized Church of Jesus Christ of Latter Day Saints (RLDS Church).

From 1865 to 1873, he conducted missionary trips throughout the Midwest, Utah Territory, and California, debating preachers of different theologies, including representatives of the Church of Jesus Christ of Latter-day Saints (LDS Church).

In a 1998 biography of Smith, From Mission to Madness: Last Son of the Mormon Prophet, author Valeen Tippetts Avery describes Smith's mental deterioration, starting with a probable breakdown early in 1870.

Avery's biography draws on a large body of Smith's correspondence and poetry to examine both his personality and his emotional state.