For a background, I generally want to see the following:
1) What would enduce your character to risk his life having adventurers?
2) What is your character's present and past employment?
3) How might the other characters know you?
4) The game is going to begin 'here'; how did you get here? Are you life long resident, a new immigrant, or a wanderer recently arrived?
That's really the minimum required to get play going at a goodly clip.
I would like to see some curiousity and invention by the player on the following, but none of it is really required, it just shows that they are thinking about the world:
5) Your character begins play with a significant amount of wealth - where did it come from?
6) What personal relationships flow from the character's current social standing (an employer, a master, a business colleages, customers, etc.)?
7) What personal relationships does the character currently value (friends, family, romantic attractions, mentors, idols, etc.)?
8) What does the character believe in?
9) Would your character be more likely to be attracted to worshiping personal household dieties with which he has an intimate relationship, or big powerful dieties emboding important ideals, or to reject religion entirely?
10) What few things would a person first meeting the character notice.
11) The day before the game started, what was your character doing?