"Cavalier" is chiefly associated with the Royalist supporters of King Charles I in his struggle with Parliament in the English Civil War. It first appears as a term of reproach and contempt, applied by the opponents of King Charles I during the summer of 1642:

Charles, in the Answer to the Petition June 13, 1642 speaks of Cavaliers as a "word by what mistake soever it seemes much in disfavour". It was soon adopted (as a title of honour) by the king's party, who in return applied Roundhead to their opponents, and at the Restoration the court party preserved the name, which survived till the rise of the term Tory.

Cavalier was not understood at the time as primarily a term describing a style of dress, but a whole political and social attitude. However, in modern times the word has become more particularly associated with the court fashions of the period, which included long flowing hair in ringlets, brightly coloured clothes with elaborate trimmings and lace collars and cuffs, and plumed hats. This contrasted with the dress of at least the most extreme "Roundhead" supporters of Parliament, with their preference for shorter hair and plainer dress, although neither side conformed to the stereotypical images entirely. Most Parliamentarian generals wore their hair at much the same length as their Royalist counterparts, though Cromwell was something of an exception. In fact the best patrons in the nobility of the archetypal recorder of the Cavalier image, Charles I's court painter Sir Anthony van Dyck, all took the Parliamentary side in the Civil War. Probably the most famous image identified as of a "cavalier", Frans Hals' Laughing Cavalier, in fact shows a gentleman from the strongly Calvinist Dutch town of Haarlem, and is dated 1624. These derogatory terms (for at the time they were so intended) also showed what the typical Parliamentarian thought of the Royalist side – capricious men who cared more for vanity than the nation at large.

The chaplain to King Charles I, Edward Simmons described a Cavalier as "a Child of Honour, a Gentleman well borne and bred, that loves his king for conscience sake, of a clearer countenance, and bolder look than other men, because of a more loyal Heart." There were many men in the Royalist armies who fit this description since most of the Royalist field officers were typically in their early thirties, married with rural estates which had to be managed. Although they did not share the same outlook on how to worship God as the English Independents of the New Model Army, God was often central to their lives. This type of Cavalier was personified by Lord Jacob Astley whose prayer at the start of the Battle of Edgehill has become famous "O Lord, Thou knowest how busy I must be this day. If I forget Thee, do not forget me." At the end of the First Civil War Astley gave his word that he would not take up arms again against Parliament and having given his word he felt duty bound to refuse to help the Royalist cause in the Second Civil War.

However, the word was coined by the Roundheads as a pejorative propaganda image of a licentious, hard drinking and frivolous man, who rarely, if ever, thought of God. It is this image which has survived and many Royalists, for example Henry Wilmot, 1st Earl of Rochester, fitted this description to a tee. Of another Cavalier, Lord Goring a general in the Royalist army, the principal advisor to Charles II, Edward Hyde, 1st Earl of Clarendon, said that he "would, without hesitation, have broken any trust, or done any act of treachery to have satisfied an ordinary passion or appetite; and in truth wanted nothing but industry (for he had wit, and courage, and understanding and ambition, uncontrolled by any fear of God or man) to have been as eminent and successful in the highest attempt of wickedness as any man in the age he lived in or before. Of all his qualifications dissimulation was his masterpiece; in which he so much excelled, that men were not ordinarily ashamed, or out of countenance, with being deceived but twice by him." This sense has developed into the modern English use of "cavalier" to describe a recklessly nonchalant attitude, although still with a suggestion of stylishness.

Oxford English Dictionary Second Edition 1989 (OED); Encyclopaedia Britannica, Eleventh Edition; OED "Cavalier", Meaning 4. attrib., First quotation "1666 EVELYN Diary 13 Sept., The Queene was now in her cavalier riding habite, hat and feather, and horseman's coate."; Carlton, Charles. Going to the Wars: The Experience of the British Civil Wars, 1638-1651, Routledge, 1994, p. 52; Hume David. The History of England from the Invasion of Julius Caesar to the Revolution 1688 (Volume V).T. Cadell, 1841, p. 216. See footnote r. cites Warwick 229; Barratt, John. Cavalier Generals: King Charles I and His Commanders in the English Civil War, 1642-46, Pen & Sword Military, 2005, 177; Memegalos, Florene S. George Goring (1608-1657): Caroline Courtier and Royalist General, Ashgate Publishing, Ltd., 2007, inside front cover; Encyclopaedia Britannica Eleventh Edition Article: GEORGE GORING GORING. Source: Wikipedia