In the past, I've talked about how to write a character background. That's a great way to build a rich character with goals and enemies and connections. But it doesn't finish the job: You still need a personality.
There are a lot of ways to generate a character personality. D&D has the famous alignment system, which I've written about in the past. The World of Darkness has Virtues and Vices (and previously, Nature and Demeanor). Other RPGs have had all kinds of other systems for helping you build your character's personality. Some give you a mechanical incentive to act a certain way. Others are a list of behaviors you're supposed to avoid or always do.
Regardless of the system the RPG you're playing uses, the best way to build a quick and memorable character personality that's easy to play and hard to forget is to use a list of absolutes.
Absolutes are behaviors your character always or never does, even when it would be pretty stupid to stick to them. And absolutes are not just for "lawful stupid" paladins (priests, detectives, officers, etc.) and stick-up-the-butt elves (ventrue, wizards, high society types etc.). Easy-going slackers and anti-authoritarian rakes have absolutes, too.
Consider the holy roller paladin who never murders sentient creatures. When the party plans to ambush some bandits, the paladin refuses to join in. "They're not hurting anyone, just walking through the forest. It's not self defense. I won't just kill them."
But also consider the foul-mouthed fighter who always mouths off to authority. "Hey your high muckety muck-ness, you got your forest cleared of bandits. Now what do I get for sticking my neck out, huh?"
Pick at least two and at most five absolutes for your character and write them down somewhere you'll always see them, such as the top of your character sheet.
Revise them to make them as short and sweet as possible. You can always explain to others that "Never Murder" means never kill a sentient living being without first giving it a chance to surrender or flee (as appropriate). But it's easier for you to write "Never Murder" on top of your character sheet, so you never forget it's there. You just need the constant reminder.
Absolutes relate to specific topics. Those topics are social norms - norms of respect, harm, autonomy, responsibility, purity, chastity, honor, honesty, politesse, etc. Your character probably doesn't have an extreme position on every cultural norm, but here's a list of common cultural norms you might have an absolute position on:
- Dignity/Vanity: ALWAYS respond to an insult. NEVER expect to be treated with respect. ALWAYS downplay my achievements and value. NEVER let someone call me anything but Sir or Sir Henry. NEVER go out in public in shabby clothing. ALWAYS exaggerate my accomplishments.
- Respect: ALWAYS call people sir or m'am. NEVER use a noble's title. ALWAYS push people's buttons and provoke them to anger. NEVER show disrespect to my elders.
- Piety: ALWAYS show respect to the gods, even the dark ones. NEVER trust a priest. ALWAYS make sacrilegious jokes. NEVER leave the dead unburied.
- Self-Control/Gravitas/Temperance: NEVER show emotion. ALWAYS try to get people to laugh and cheer. NEVER talk about my family because it hurts too much. ALWAYS cry when someone I know dies. NEVER repeat myself unless asked to. ALWAYS go straight to death threats when things don't go my way.
- Forgiveness: NEVER forgive a wrong. ALWAYS forgive and forget wrongs against myself (never against innocents).
- Chastity/Purity: NEVER drink alcohol or take drugs. ALWAYS get blitzed between adventures. NEVER turn down seductions. ALWAYS flirt with attractive NPCs.
- Prudence/Recklessness: ALWAYS touch the shiny. NEVER walk into a situation without an exit plan. ALWAYS get it in writing. NEVER trust an elf. ALWAYS trust women. NEVER compromise (my way or the highway). NEVER make a threat I'm not willing to carry out.
- Exchange: ALWAYS return a favor immediately (NEVER let someone have a debt over me). NEVER do something for nothing. ALWAYS give generously, tip generously, and share my wealth generously.
- Courage: NEVER stick my neck out for a stranger. ALWAYS protect those weaker than myself, even unto death. NEVER kill a fleeing foe. ALWAYS be the first through the door. NEVER ask someone to do something I wouldn't. ALWAYS avoid scandal and shame.
- Loyalty: NEVER let a friend down. NEVER make promises. ALWAYS look out for number one - everyone else can go to hell. ALWAYS repent for a mistake.
- Honesty: NEVER tell a lie. ALWAYS try to convince people I'm on their side. NEVER pretend to be who I'm not. ALWAYS seal a bargain with a drink. ALWAYS punish people who break their promises to me.
How Absolute is Absolute?
The mood of the game you're playing in will set how absolute your rules should be.
Superheros get to have absolute ethical boundaries that always seem to work out in the end. No matter how dumb it seems that Batman doesn't just kill the Joker, it still works out OK because even if the Joker escapes Arkham, Batman always catches him again before he pulls off some horrible scheme.
But in a horror game, you're damned if you do, damned if you don't: If you act against your instincts under pressure, you'll suffer for it. If you stubbornly stick to your bad habits or morals, you might become a martyr to them.
Gritty mood games tend to push your boundaries, offering you chances to break from your absolutes and have your character evolve, or else suffer for their decisions (both of which are interesting developments). The ethical paladin becomes more of a cold-blooded pragmatist and is judged for it. The mouthy rake learns when to hold their tongue and grows as a person.
Your character might grow and change. Absolutes give you a great opportunity to do so! When you encounter a situation where your absolutes are tested, you can choose to act according to your absolutes and suffer the consequences or act against them and grow as a character.
If you stubbornly martyr yourself to your absolutes, you can choose to see the effect it had and regret it or defend your principles to the last. If you stray from your absolutes, you can regret it and see it as a one time mistake, or you can realize you've been wrong all along and evolve as a person.