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.

A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material to heat water in the locomotive's boiler to the point where it becomes gaseous and its volume increases 1,700 times. Functionally, it is a steam engine on wheels.