William Gilpin (October 4, 1813 – January 20, 1894) was a 19th-century US explorer, politician, land speculator, and futurist writer about the American West. He served as military officer in the United States Army during several wars, accompanied John C. Frémont on his second expedition through the West, and was instrumental in the formation of the government of the Oregon Territory. As a politician and writer, he was an inveterate believer in Manifest Destiny and was a visionary booster of new settlement to the West, helping lay the groundwork in his writings for a modern theory of the succession of civilizations. He served as the first governor of the Colorado Territory, where his administration was consumed largely with the defense of the new territory in the early days of the American Civil War and was brought down after only one year by scandalous financial dealings. After the demise of his political career, he made a large fortune as a land speculator in New Mexico, although his dealings were questionable and possibly illegal.