I got thinking about this when I started to read "The Knight of the Burning Pestle." I don't recall hearing of many knights during Elizabeth's time or even in much of the Tudor reign, historically, but the ones I read about in that era seem to be made a mockery of (Knight of the Burning Pestle, Don Quixote, etc). Thinking about it (from my fairly superficial literary historical knowledge), they went from thane-like warriors to Arthurian/Chaucerian knights that seem to blend both battle and romance (how accurate that knight is, I'm not sure), and then they seem to more or less disappear except to be used as a medium of humor as we move into the renaissance from the literature I read. But they do still exist today--just as people of esteem not necessarily having anything to do with war or even the crown/court. I was mostly wondering when and why the transition(s) took place. The orders listed on the link are interesting--but they don't acknowledge the knights/any order before the 18-19th century.
A similar thread occurred a few months ago, but the answers nearly all focused on the different orders of knighthood, and none of those orders were before the 18th century. I'm looking for earlier development.
This post explores the early development of knighthood fairly well.
But as it does not go much beyond 1200, I'll speak briefly about the changing status of knights in the 14th and 15th centuries. If one of our late medieval flairs would like to chime in with more detail, I would be very grateful (I do the High Middle Ages mostly).
The 13th century is really both the peak and the beginning of the end for knights, in different ways. It's a great time for chivalry and the knightly arts, all of which are further developed, but it's also the start of their demilitarization as a class. The rising costs and obligations of knighthood reduced the number of men who could afford to become so entitled, and inversely, those who did become knights tended, as an aggregate, to be wealthier than the knights of the 11th and 12th centuries.
By the 14th century, most of the military function of "knights" is being performed by esquires, armigers, and men-at-arms; that is to say, men of gentlemanly background who possess horse, armor, weapons, and military training, but not the title of "knight." Knighthood has really lost the last vestiges of its status as "the class that fights". Knights still fight in the wars of this period, just as noblemen do, but in the case of the former, they've risen in status; they tend much more than in the past to be leaders of men rather than individual combatants, and have in effect become petty nobles. If we look at the English armies of the HYW period, it is very common to find groups of archers and men-at-arms serving under a single knight; or, just as likely, serving under a senior man-at-arms.
Turnbull, Stephen. The Knight Triumphant.
France, John. Mercenaries and Paid Men: The Mercenary Identity in the Middle Ages.