While by no means the first steam locomotive, it can be argued that George Stephenson's famous Rocket was the first truly successful one.
Drawing on George Stephenson and his son, Robert's, experience building earlier locomotives such as the Locomotion and Lancashire Witch, Rocket embodied the best locomotive practice of the day, and was the deserved winner of the Rainhill Trials held by the new Liverpool and Manchester Railway to select the locomotives to be used on the new line.
Indeed, the general principles laid down by Rocket in 1829 were followed in the vast majority of steam locomotives ever built. Rocket's boiler was longitudinal, clad in insulating material (wood, in this case), with a firebox at the back; the hot gases from the fire passed through a number of fire tubes through the boiler water, instead of a single flue as on all earlier locomotives. Exhaust steam from the cylinders was expelled through an exhaust nozzle to provide a forced draught for the fire.
Like the majority of steam locomotives to follow, Rocket had two cylinders, though their placing, angled upwards and backwards, was not to be continued; indeed, Rocket itself was later modified with more horizontal cylinders. Most subsequent locomotives had cylinders oriented horizontally forward of the first driving wheels. Rocket's cylinders also acted directly on the driving wheels, unlike most previous designs that had a complicated system of levers to transfer the force.
Rocket's fuel and water was, again in a pattern much duplicated, carried in a tender hauled behind the locomotive.
Emerging triumphant at the Rainhill Trials, Rocket was purchased by the railway company. Within a couple of years, modifications were carried out to bring it up to the standards of later engines; the cylinders were made more horizontal, a smokebox was added, and the towering stack was shortened.
In this condition it is preserved, in the Science Museum in London.