John Bull is a historic British-built railroad steam locomotive that operated in the United States. It was operated for the first time on September 15, 1831, and became the oldest operable steam locomotive in the world when the Smithsonian Institution ran it under its own steam in 1981. Built by Robert Stephenson and Company, it was initially purchased by and operated for the Camden and Amboy Railroad, the first railroad in New Jersey, which gave it the number 1 and its first name, "Stevens". The C&A used it heavily from 1833 until 1866, when it was removed from active service and placed in storage.

Under the Whyte notation for the classification of steam locomotives, 0-4-0 represents one of the simplest possible types, that with two axles and four coupled wheels, all of which are driven. The wheels on the earliest four-coupled locomotives were connected by a single gear wheel, but from 1825 the wheels were usually connected with coupling rods to form a single driven set.