Chivalry was invented by Sir Gent L. Man who was a knight in the medieval period. The code was designed to resolve disputes over women between men but later evolved into general etiquette.
The first known entry is as follows: "If ye and ye brethren both covet a wench then ye must not commence a clash of swords. For he who triumphs in a clash of tongues shall emerge victorius." This basically means that you fight with words not fists.
This then evolved to a basic set of codes for knights or "brethren." The general treatment of women and etiquette was not developed until later on.
The first mystery is how the knight's armour evolve into the traditional gentleman attire and beverage. The first theory is that a top hat symbolises the massive heart of a gentleman and the suit came from a 'suit' of armour. This is a widely accepted theory. However, my hypothesis is that gentlemen must of be seen as to soft for knighthood and their suit of armour became just a suit. The hat probably symbolises the old helmet that knights wore.
The next mystery is very controversial. The gentlemen disappeared between medieval times and the 18th century. The cause is unknown which is the cause of the controversy... I think that tea caused the arrival of gentleman which would solve this mystery. However, others think that chivalry constantly fluctuates in popularity hence why they disappeared and why it has dropped yet again today.
Tea is an unusual beverage which probably caused the spike in gentlemen. This beverage probably creates ideology which allows a man to put a woman's interests before his own. Additionally, coffee drinkers are less chivalrous than tea drinkers. Thus, coffee counteracts the effects of tea which probably explains the drop of gentlemen in the 20th century. It's true because coffee makes people much more cranky. This was originally a mystery until I resolved it. Obviously.
The final mystery is how chivalry evolved into etiquette. There are no known theories, only conjectures (guesses). Some say that it must of been natural evolution (since treatment of 'brethren' must also apply to women) while others say etiquette was created with chivalry. This divides into two groups; evolutionists and creationists. None are right of course since there is no valid evidence either way.
I hope you have learned loads about Gentlemen and/or this helped broaden your intellect (or lack thereof).