Son of former Nez Perce tribal chairman Richard Halfmoon, Otis grew up amid the plateaus and river valleys of his community's Idaho homeland and is a native speaker of the Nez Perce language.

After service in the U.S. Army, Halfmoon joined the National Park Service. Over the past two decades he has worked as an interpreter, park historian, unit administrator and liaison officer with indigenous peoples across the western states. Halfmoon is committed to the documentation and preservation of Nez Perce history and culture.