There is a lot to be said about Oscar. Sure, he doesn't get much lime-light, but he does the single most important act for you in the game. The act I am talking about is giving you the key to your freedom. Without this key, we would have just rotted away.
Oscar basically wants to be "us" as the player. He wants to be the chosen undead, destined save the world. Unfortunately he couldn't do that, but he isn't selfish, he lets you take the seat of the main protagonist.
Also he wears the "Elite Knight" Armor. As many of you know, this is some good stuff. Many consider it to be the armor of choice due to its good defenses, mild weight, and lack of stamina hindrance.
I know that everyone loves SunBro, OnionBro, WolfBro, and the likes. But try to remember the guy who started it all... Oscar, Knight of Astora!
^It is the same guy. Also i've come the conclusion that his armour (Elite Knight set) is actually the armour featured on the front cover of the NA/EU edition, although it is slightly jazzed up in the picture it is the closest match.