I created a character a while ago, called Xi Xiu. She's not my favourite character, but she's the one I use the most. What makes her so special to me, and so reusable, is how diverse she can be. Her story and personality change, to suit the setting, but there are always a few constant threads, that define who she is.

She's Chinese-American, and very oddly proportioned. She's not necessarily attractive physically, but rather her confidence makes her attractive. She's short, skinny, with a large forehead, a tiny nose, and has an obsession with some overly specialized category of weaponry, and always has a weapon with her that carries emotional significance. She stares at things in an odd way. Usually, she has an obsession with revolvers, but she's be written to only use knives, swords, rifles, or even her bare hands. 

She's jaded, and doesn't know her parents. She was raised by someone with no familial relation to her, who is no longer in the picture for one reason or another. She was once the property of a government or corporation, for one reason or another. She has bodily enhancements under her skin. They're usually to strengthen her bones, or improve her vision and aim. She has a dream for a simple life, but believes herself to be forever bound to her work. 

She likes leather and denim, and has a lucky article of clothing with her. It's usually either a pair of sunglasses, or a bandanna.

Her face is pale, for one reason or another. It doesn't suit her. 

She's desensitized to pain, and has many scars under her clothes.

Her best friends are criminals, or homeless. She usually has multiple sidekicks, of sorts, just to give the impression that she has influence in an organization.

She shaves all or part of her head, for comfort, and to intimidate people. If she can't shave her head, for whatever reason, she likes to use gel and elastics to make the sides of her head stick out, to give the impression that her head has wings.

She goes by a single compound word as her nickname. "Gunrat", "Hellcat", "Bingbing", "Bugeyes".

She likes bright spring dresses, and traditional things, but never wears them. She prefers hot weather and open environments.

She will eat anything, smoke anything, but refuses to get drunk.

Her favourite colour is green, but she usually wears black and blue. 

She doesn't like swimming, and hates flying. She does enjoy singing, however, but her voice isn't particularly great.

She speaks many languages. If she didn't become a fighter or adventurer of sorts, she would have been a translator or international dignitary.