Well, first we'd need to know what origin this character is, ex- mutant, science, etc.
Another thing that I would have to ask is... where did your character come from? That usually helps a LOT in making these descriptions easier.
Yep, I agree... add anything you have in your brain already for the concept [what's there already is good fodder], and the whizzes here will go to work, I suspect. 
Let me first say hello to everyone, and secondly if this is in te wrong forum I do appologize.
I'm an on again off again type of RPer and I have created a concept toon "WidowWarrior" DM/Invuln on pinnacle and I absolutely SUCk at writing short descriptive stories about the origions of my toon's. What I was wonderingwas if one of you creative RPers could please help write a description for WidowWarrior. I would ofcourse put your forum name at the end of the description to give you the credit you'd deserve and if you wanted I would be more then willing to pay 5million infamy (If you happen to be on pinnacle) for your time and efforts.
His name (WidowWarrior) is pretty descriptive already of who he owes his allegeances too. The concept is that he deeply loves Ghost Widow and is more then willing to die trying to fullfill any task she set's before him.
Hopefully this is descriptive enough of a concept.
I thank you in advance for ANY help you all might be able to offer