Isaac Asimov,
Letter to Planet Stories, Jan 1951
(1951)
“ When I wrote "The Mule" in 1945, I needed a name for a planet. It was wartime and there was a large map of the Far East on the wall. Kalgan was on the map. It is the name of a sizable city in the province of Chahar (Inner Mongolia) , which is located about one hundred miles northwest of Peking. ”
