John of Bohemia

“Encyclopædia Britannica entry”

“Before he set off, he was reported to have said, “Let it never be the case that a Bohemian king runs from a fight.” His gesture was not entirely in vain. According to tradition, the King of England's son, the "Black Prince", was so impressed by this display of lunacy that he decided to adopt King John's personal crest of three white ostrich feathers and his motto "Ich Dien" (I serve) as his own. It is the Prince of Wales's motto to this day.”

“The manner of his death gave rise to the obsolescent idiom, “to fight like King John of Bohemia”, meaning “to fight blindly””

“Absit, ut rex Boemie fugeret, sed illuc me ducite, ubi maior strepitus certaminis vigeret, Dominus sit nobiscum, nil timeamus, tantum filium meum diligenter custodite.”