IRAS F15307+3252: A Hyperluminous Infrared Galaxy at Z = 0.93

A new hyperluminous infrared galaxy in the IRAS Faint Source Catalog is identified at a redshift of 0.93. This object has a bolometric luminosity of ~10^13^ L_sun_, a very large ratio of infrared-to-optical luminosity, warm dust emission, a ratio of infrared-to-radio flux densities consistent with other infrared galaxies, and an optical spectrum similar to a Seyfert 2 galaxy. IRAS F15307+3552 shares these characteristics and its radio-to-optical spectral energy distribution with two other infrared galaxies, F10214+4724 and P09104+4109. Discovery of a third object with these properties defines an extreme subclass of ultraluminous galaxies powered primarily by star formation. The systematic method used to find this object begins the process of determining the space density of these most luminous examples of the infrared galaxy phenomenon.