Let's talk about character classes some more, specifically, Knights and Fighters, Paladins and Rangers.
First off, there is no such class or sub-class called "Knight" in AD&D 1e. It doesn't exist.
Having said that, there are two types of classes specifically referred to as Knights in their descriptions, Clerics and Paladins. We talked about those earlier.
However, In the Class of Fighter, three types are presented, the basic Fighter, the Paladin and the Ranger.
Here's my take on those fighters, but first, a word about Knights.
A Knight is a social class identification. It does not indicate one's profession as a warrior or soldier, etc... The main ways one is Knighted is to come from a highborn family of Knights, to join an order that establishes Knighthood on it's members or to be a conquering hero that is Knighted by his/her liege lord for spectacular service and duty.
All of those are changes in social status.
Historically, for just a moment, many noble-born families lost their riches but kept their status. They could hardly afford proper weapons and armor, and often did not much more than enter tournaments. Yet these were accorded every perk of Knighthood none-the-less.
A truly skilled fighter and warrior could have struck it rich in found treasure and bought the best weapons and armor, yet still would not be recognized as a Knight if they didn't meet any of the above listed ways of gaining Knighthood.
The Fighter class is exactly that warrior or trained soldier who has spent years in training and battling, honing the one thing they do best, battle. A Fighter may someday, somehow be Knighted but the odds are against them and they likely prefer to be free spirits anyway, un-beholden to a liege lord.
Often times in AD&D 1e, Players hold a view that Fighters are like Conan the Barbarian. They most certainly can be like that, but that is not necessarily what they are limited to. Fighters have the broadest range of background and employment of their skills of all the fighting classes. They certainly could be a Knight. I see them as the most likely to have to earn Knighthood if that is what they seek by their valor and deeds on the battlefield.
The Paladin, as discussed earlier, is a Knighted character and is a subject to his king or liege lord. As DM, I let Players know that Paladins as PC's must have a background story that indicates their status and how they attained their Knighthood. Who their lord is and who their deity is. Typically, I see Paladins as coming from noble families that have served their King and country as nobility for many years.
Rangers are something interesting as a sub-class of Fighter. Rangers are kind of like a Paladin for Druids. Not quite exactly though. Like Paladins, they do not attract men-at-arms, but at some point do get to have henchmen and hirelings.
Also, Rangers do get to employ Magic Users spells as well as the Druid spells eventually. Rangers MUST be of a good alignment though. I personally like to place Rangers in the company of Druids as Henchmen because they work so well together. Rangers, like Fighters, are not required by me to provide a social class and listing like Paladin are in their background.
I see Rangers as very much in the Guerrilla warfare type. While they can be effective indoors, it's the outdoor world in which they can do their best work. it's where they are most at home. I don't really see Rangers seeking Knighthood myself. They would likely enjoy their liberty and freedom to be their own Master.
In regard to Knights, that leads me to say that Clerics are the primary ones to achieve their status through joining an order of a religious nature, like the Templar Knights. Not to say it is limited to them in this way, but that I think they are the ones most likely to accomplish it in this manner.