The title most often utilized for Korean rulers is king and not emperor.
Department of Asian Art, The Metropolitan Museum of Art
October 2004
Department of Asian Art. “List of Rulers of Korea.” In Heilbrunn Timeline of Art History. New York: The Metropolitan Museum of Art, 2000–. http://www.metmuseum.org/toah/hd/koru/hd_koru.htm (October 2004)