One of my teachers told me a story of a European king or Lord or something who was blind. He would ride into battle, swinging his flail around blindly, while a squire would lead his horse forwards. The horse was trained to keep its head perfectly straight, otherwise the flail would hit it. He had multiple horses at ready at the edge of the battlefield incase his horse was taken out by the enemy, or if he took it out with his flail. At the end of the battle, the enemy King found his body, dead, surrounded by bodies he had killed. The King, with incredible respect towards the blind king/lord/guy, took his coat-of-arms as his own. This story sounds awesome, but a bit too amazing that I've never heard it from anywhere else. There's also a lot of stuff that seems, odd. For example, why did no archers shoot at him, being the general. Or how did he get back on a horse being blind and in a battlefield? The teacher is a member of HEMA and has a lot of experience under his belt (was a 'King' at one point), but is this story true?
Whether you believe this story or not depends on whether you believe the chronicler who recounted it. The Chronicles of Froissart, by Jean Froissart (c.1337–1410?), recounts the following story regarding the battle of Crecy between the French and the English during the Hundred Years' War:
The valiant king of Bohemia called Charles of Luxembourg, son to the noble emperor Henry of Luxembourg, for all that he was nigh blind, when he understood the order of the battle, he said to them about him: ‘Where is the lord Charles my son?’ His men said: ‘Sir, we cannot tell; we think he be fighting.’ Then he said: ‘Sirs, ye are my men, my companions and friends in this journey: I require you bring me so far forward, that I may strike one stroke with my sword.’ They said they would do his commandment, and to the intent that they should not lose him in the press, they tied all their reins of their bridles each to other and set the king before to accomplish his desire, and so they went on their enemies. The lord Charles of Bohemia his son, who wrote himself king of Almaine and bare the arms, he came in good order to the battle; but when he saw that the matter went awry on their party, he departed, I cannot tell you which way. The king his father was so far forward that he strake a stroke with his sword, yea and more than four, and fought valiantly and so did his company; and they adventured themselves so forward, that they were there all slain, and the next day they were found in the place about the king, and all their horses tied each to other.
A note on the names. Charles of Luxembourg is known to history as John of Bohemia. The noble emperor Henry of Luxembourg is Henry VII, King of Germany and co-ruler along with his father Frederick II, Holy Roman Emperor (that is until daddy deposed him in favor of his half-brother). Lord Charles (in the text as "the lord Charles, my son") is Charles IV, Holy Roman Emperor, aforementioned half-brother of Henry VII, and successor to Frederick II as Emperor.
As for the part about the coat of arms, that appears to refer to the Prince of Wales' feathers, which have the motto ich dien (German: "I serve"). I cannot find a reputable source that confirms this part of the story, and fwiw, the Wikipedia page on the subject seems to think it's a myth, citing a work from a historian of British heraldry from 1929.