How do you want your character to be recognized? What makes him or her different from the rest of the characters in the game? Your personality might be the most important part of creating a profile. A player isn't defined by his race or powers, but his level of charisma and morality. A character's personality defines how he will react to a given situation. If the evil warlord is advancing upon you with a flaming sword, do you risk your life and take him on, or do you run away screaming? (I'd actually like to see the latter happen just once.

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So, first thing's first. Morality. Your character's morals are probably the second thing you will think of in creating a character and they influence what you decide the character's background will be. (The first thing being the cool powers he or she will have.

) I'll be borrowing the D&D alignments for this since they define things rather nicely. There are two axis' that make up your moral compass. You have one, which ranges from good to evil, and another that ranges from lawful to chaotic. Neutral lies inbetween both axis'.
Good: If you are a good character, you strive to aid and protect those in need. While you aren't required to fulfill this obligation in every circumstance, it should be a priority for your character. A lawful good character places a great deal of faith in authority and law. He is suceptible to following an evil ruler blindly, but he also makes a better leader than most personality types. He embraces the ideal of diplomacy and cooperation, but has difficulty in making his own choices.
A neutral good character lacks the loyalty to government, but does not go out for the purpose of bringing the king grief. He merely seeks to do what he can to make the world a better place to live in. A cleric who tends the wounded regardless of their deeds and financial status defines the morality of a neutral good character quite well.
Robin Hood should come to mind when thinking of a chaotic good character's personality. A chaotic good character is your classic rebel, always seeking to liberate those under any percieved oppression. He doesn't have to denounce all authority, but he will be the most vocal when he sees an injustice. A chaotic good character would tend to be a poor leader due to a lack of organizational skills, though most do tend to try to rally the oppressed to help.
Neutral: A pure neutral character is not an inactive one, as the name might suggest. The neutral character merely has no loyalties whatsoever towards anything but himself. This might be a good place to start your character as, and then allow him to evolve into a different alignment as you discover more about what fits his personality and your preferred play style. Or you might see yourself as above morality. A hired mercenary who takes any job would fit this bill.
Evil: Regardless of your probable preconceptions about an evil person, he does not always seek destruction by nature. He is, however, inclined to take what he can at everyone else's expense, and often, thier lives. A lawful evil character is in many ways like a lawful good character. He is a good leader, and believes in a heirarchy of power. However, his ideas on how this heirarchy should run are different. He will have no problem exploiting the public through unfair taxes and slave labor.
A neutral evil character is prone to take advantage of others for his personal gain, but lacks the will to do it on a mass scale. He will only look out for himself and duck away at any sign of danger.
A chaotic evil character is the lowest of the low. Your typical thug who takes pleasure in killing weak victims to satisfy his bloodlust. A leader among these sorts of people is only leader until he is assassinated. When danger comes, he will generally fight to the death.
Charisma levels is also a major factor. At high levels, you are the life of the party, able to have the opposite sex do advanced acrobatics at a command. You are bright and optimistic about any situation, and probably able to talk your way through any trouble you might encounter. At charisma's low, you are brooding and antisocial. No one likes you and you probably don't mind that too much. You are pessimistic and tend to spread gloom in your wake. Such characters tend to have to fight their way out of trouble more often than a character with more grace of tongue.
A character with personality will also have various quirks that will affect what he says and when. A proud elf for example might shout "The elves are upon you!!" at the beginning of a battle. In your typical conversation, your character might be restless and must constantly be moving, and while fidgiting around might annoy the other character, it adds an amount of realism to your character. The closer to making your character 'real' you get, the more he is remembered. He becomes more likely to have an effect on other characters plots because the other characters and players remember you and will come to you for help in progressing some aspect of their own story line.