John Ericsson (born Johan) (July 31, 1803 – March 8, 1889) was a Swedish-American inventor. He was active in England and the United States.
Ericsson collaborated on the design of the steam locomotive Novelty, which competed in the Rainhill Trials on the Liverpool and Manchester Railway, which were won by George Stephenson's Rocket. In America he designed the US Navy's first screw-propelled steam-frigate USS Princeton, in partnership with Captain Robert Stockton, who unjustly blamed him for a fatal accident. A new partnership with Cornelius H. DeLamater of the DeLamater Iron Works in New York resulted in the first armoured ship with a rotating turret, USS Monitor, which dramatically saved the US naval blockading squadron from destruction by an ironclad Confederate vessel, CSS Virginia, at the Battle of Hampton Roads in March 1862.