Ironside was the name given to a trooper in the cavalry formed by English political leader Oliver Cromwell in the 17th century. The name came from "Old Ironsides", one of Cromwell's nicknames.

Cromwell trained and equipped the troop early in the English Civil War. The troop formed the nucleus of the New Model Army. The Ironsides' use of armour and their disciplined formation and obedience to their commanders, at a period when the majority of both armies consisted largely of ill-equipped rabble, made them virtually invincible.