Cyrus Reed Teed (October 18, 1839 – December 22, 1908) was a U.S. eclectic physician and alchemist turned pseudoscientific religious leader and self-proclaimed messiah. In 1869, claiming divine inspiration, Teed took on the name Koresh and proposed a new set of scientific and religious ideas which he called Koreshanity, including the belief in the existence of a concave, or "cellular", Hollow Earth cosmology positing that the sky, humanity, and the surface of the Earth exist on the inside of a universe-encompassing sphere.
In New York in the 1870s, he founded the Koreshan Unity, a commune whose rule of conduct was based on his teachings. Other similar communities were established in Chicago and San Francisco. After 1894, the group concentrated itself in the small Florida town of Estero, seeking to build a "New Jerusalem" in that locale, peaking at 250 residents during the first decade of the 20th century. Following Teed's death late in 1908 the group went into decline, finally disappearing in 1961, leaving the Koreshan State Historic Site behind.