I started thinking about this the first time I watched Angel and noted the scope of Wolfram & Hart. Why didn't his Big Bad get replaced each season, like Buffy's did? For that matter, why lawyers?
The answer is in each title character's theme. Buffy is a real human, trying to live a normal life. Angel is anything but. His affinity with the type of monsters that emerge from the Hellmouth prevent him from using them in the classic image of counterbalance. Wolfram & Hart is evil while Angel is good, yes, but the crucial difference that makes them true opposites is this: they're a lawful organization, while he's a chaotic hero.
Even if you haven't played D&D before, those descriptions might sound familiar to you-- they're convenient, and geeks like me have implemented them in all fandoms for many years. The fantasy genre and its many mutations are traditionally full of exaggerated portrayals of good and evil, so these archetypes tend to show up there, just waiting to be identified. If you've never heard of D&D or its character alignment system, though, let me start by quoting from my Player's Handbook.
Good and evil are not philosophical concepts in the D&D game. They are the forces that define the cosmos.
Devils in human guise stalk the land, tempting people toward evil. Holy clerics use the power of good to protect worshipers. Devotees of evil gods bring ruin on innocents to win the favor of their deiies, while trusting that rewards await them in the afterlife. Crusading paladins fearlessly confront evil-doers, knowing that this short life is nothing worth clinging to. Warlords turn to whichever supernatural power will help them conquer, and proxies for good and evil gods promise them rewards in return for the warlords' oaths of obedience.
A character's or creature's general moral and personal attitudes are represented by its alignment: lawful good, neutral good, chaotic good, lawful neutral, neutral, chaotic neutral, lawful evil, neutral evil, and chaotic evil.
Ring any bells? Consider those terms for a little while and see if you don't start coming up with examples from your favorite work of fiction. One word of caution, though, which I'm sure doesn't need to be said: avoid applying the system to anyone or anything that exists in real life. The point is to understand and discuss the motivation and themes of characters, not to pick sides. Obviously, this exercise is by nature an oversimplification of very complicated ideas, and even the characters I chose to represent each one are going to deviate from their molds a great deal, not to mention the way they change over the course of a series (in true Whedon fashion).
If the categories make sense to you, I'd love to be challenged on my choices, and if you think of any characters or organizations that I missed, tell me where you think they should go! For starters, I'm going to pick what I think is the best representation of each alignment, explain why, and add a few other representatives.
Lawful Good: Giles. From the beginning of the show, his major drive has been doing the right thing at any cost, including harm to those he loves (and he does love very deeply). Until he's fired from the Council, he works within their framework without any attempt to challenge it, and even afterward, he prefers to have a system for every part of his life. Authority might grate on him, but order is essential. (Eventually, his lawful side does diminish, of course.)
Other examples: Kendra, Joyce, Tara, Riley
Neutral Good: Buffy. Soon after she reaches adulthood, she leaves the institution meant to control her, but it's not a simple act of rebellion-- Buffy's always going to devote herself to saving the world and the people in it, just as her destiny says she should. What separates her from law is that she doesn't need destiny to dictate. She chooses to do good for its own sake, her power being simply the tool that allows her to make that choice.
Other examples: The Scoobies, Lorne, Anne, AtS5 Connor, Andrew
Chaotic Good: Angel. Considering that he doesn't legally exist, chaos might be seen as his only option, but I think it runs much deeper than that. Unlike Buffy, Angel's very nature contains elements that he actively seeks to avoid, forcing him to swim upstream just to remain in the state he's chosen. He desperately wants to help people, but the rules laid out by society have ceased to matter; at this point, he can only answer to his own soul.
Other examples: The Fang Gang, AtS5 Spike
Lawful Neutral: Anya. After a thousand plus years of humanity, then vengeance, then humanity...can you believe how little she changed? Yes, Anyanka displayed some truly evil traits, and we definitely saw Anya coming into her sense of ethics by the end of the series, but it was far too gradual to line up with the coming and going of her demonism. Good vs. evil were secondary for her. Law came first: justice and punishment. And capitalism.
Other examples: The Watchers' Council, BtVS3 Wesley
Neutral: The Initiative. At first I had them pegged as lawful, thanks to the government connection, but that connection was tenuous at best. From what we saw of them in S4, the Initiative was concerned mostly with researching and executing their own projects. They were too self-contained to be lawful or chaotic, and the range of humans affiliated with them showed that the organization itself couldn't be evil and wasn't overly concerned with good.
Other examples: Clem, Jonathan, Doyle, Whistler, Holtz
Chaotic Neutral: Faith. We've been watching her switch sides since she appeared, and each phase is tempered by her inability to pick a self and be comfortable with it. She can't just do the right thing without thinking about what it means for her life, but she also can't stay bad even if she tries. Ultimately she ended up good, but in the meantime, what hasn't changed? Faith is her own girl. The problem with authority figures never went away, and if you try anything she will stab you with this fork.
Other examples: Ripper, pre-AtS5 Connor
Lawful Evil: Wolfram & Hart. There's hardly anything that needs to be said about Wolfram & Hart aside from 'lawful' and 'evil'. Next!
Other examples: The Mayor, Harmony, Principal Snyder, Pylean government, Jasmine
Neutral Evil: Warren. Evil doesn't entail a devotion to choosing wrong over right; in simplest terms, it's nothing more than total selfishness. Ideas of chaos and order can only steer the way it's expressed, and Warren has no thought for upsetting anyone's balance or building a system to spread his ideology-- he's in it for himself. His mind is still entirely human, but he's taken it to its lowest point in our morality spectrum.
Other examples: Amy, Glory, the First Evil
Chaotic Evil: The Fanged Four. They have a pecking order amongst themselves, but not one of them will ever back down and surrender their power to any one of the others. Darla loves a natural disaster, Angelus rejects Aurelius immediately, Drusilla is crazy, and Spike hardly even sees his victims as long as they provide the opportunity for violence.
Other examples: Dark Willow, most vampires, Ethan Rayne