I want to say that although they touched some good points, they forgot the main way to differentiate characters in any RPG, especially Old School RPGs: Through playing the game. In a game where you literally take the whole of this completely different person, the way you play them is what really differentiates them.
So, for me, the major ways to make your character different is through these following things:
Personality and Mannerisms: A brash and cocky fighter is very differently than an centered and calm one. The same character can be very different if he is always sharpening his weapons obsessively or if he likes to talk to his weapons as if they were people.
If you need, here is a link to a big list of personality traits: http://ideonomy.mit.edu/essays/traits.html
And here a list for mannerisms: http://www.jacibyrne.com/2013/06/19/a-list-of-mannerisms-for-writers/
Former Occupation: What did your character do before becoming a greedy adventurer? This can shape how they see the world, what they know and how others see them. A farmer could know a little about plants and animals, but wouldn’t be as respected as a former sheriff or town guard. The way the character left their former occupation might also change things. Did he left it willingly or was he exiled from his home village?
Here is a list of common medieval occupations: http://www.svincent.com/MagicJar/Economics/MedievalOccupations.html
Ambitions and Complications: One of the main things that define who we are is what we want. A grim mercenary looking for his next pouch of gold plays really different from the former soldier trying to rebuild his reputation. Your problems also shape you. Do you have an addiction? Are you afraid of something. Does someone hates your guts? Often starting with a problem help differentiate your character and can give the Referee something to male the game more personal to your character.
If you need a list of complications, Sharp Swords & Sinister Spells has a generator for that!
Past Deeds: After a few game sessions, the things your character did in the game will also help determine who they are. After coming back from a haunted ruins bearing sacks of coins, they start to attract attention and gain fame. This might be good or bad. If they steal the inhabitants of the small town, they will be criminals and not heroes. Along the way, they will make friends and enemies (or just contacts, which is also very useful). This will all shape them.
In the end, for me at least, differentiation is more about how we play the game than how the game rules are set up. I prefer to concentrate my efforts and time for the actual game as it happens, not outside it writing huge backgrounds or creating an elaborate build that takes me three hours to complete. I think that’s why I like BX D&D so much...
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