Roundheads were the supporters of the Parliament of England during the English Civil War (1642–1651). Also known as Parliamentarians, they fought against King Charles I of England and his supporters, known as the Cavaliers or Royalists, who claimed rule by absolute monarchy and the principle of the divine right of kings. The goal of the Roundheads was to give to Parliament the supreme control over executive administration of the country/kingdom.
Most Roundheads sought constitutional monarchy in place of the absolute monarchy sought by Charles; however, at the end of the English Civil War in 1649, public antipathy towards the king was high enough to allow republican leaders such as Oliver Cromwell to abolish the monarchy completely and establish the Commonwealth of England.
The Roundhead commander-in-chief of the first Civil War, Thomas Fairfax, remained a supporter of constitutional monarchy, as did many other Roundhead leaders such as Edward Montagu, 2nd Earl of Manchester, and Robert Devereux, 3rd Earl of Essex; however, this party was outmanoeuvred by the more politically adept Cromwell and his radicals, who had the backing of the New Model Army and took advantage of Charles' perceived betrayal of England in his alliance with the Scottish against Parliament.
England's many Puritans and Presbyterians were almost invariably Roundhead supporters, as were many smaller religious groups such as the Independents. However, many Roundheads were members of the Church of England, as were many Cavaliers. Roundhead political factions included the proto-anarchist/socialist Diggers, the diverse group known as the Levellers and the apocalyptic Christian movement of the Fifth Monarchists.
Some Puritans (but by no means all of them) wore their hair closely cropped round the head or flat. There was thus an obvious contrast between them and the men of courtly fashion, who wore long ringlets. During the war and for a time afterwards, Roundhead was a term of derision, and in the New Model Army it was a punishable offence to call a fellow soldier a Roundhead.