John Mullan Jr. (July 31, 1830 - December 28, 1909) was an American soldier, explorer, civil servant, and road builder. After graduating from the United States Military Academy in 1852, he joined the Northern Pacific Railroad Survey, led by Isaac Stevens. He extensively explored western Montana and portions of southeastern Idaho, discovered Mullan Pass, participated in the Coeur d'Alene War, and led the construction crew which built the Mullan Road in Montana, Idaho, and Washington state between the spring of 1859 and summer of 1860.