A little bit of history, a little bit of mystery

For you writers out there, how well do you know your characters before you write them?

For you readers, how much of the character's past do you really want to know?

I get the idea that authors need to know their characters.  Unfortunately, I have a tendency to want to share all that I know!  So how much history do readers want?  Do you want to know what makes my antagonist do what he or she does?  What makes them into murderers and such?  Or is it enough to know why my protagonist feels the need to help bring the killer to justice?

To be honest, I don't always know what motivates my characters.  Maybe that's why I want to share the things I do know.  As a writer, it's enough for me to know what makes my antagonist act at the moment.  As a reader, I am usually OK with that, as well.  I want to know how and why the crime was  committed, but I don't necessarily need to know everything that led the "perp" to that moment.

Its almost like a balancing on a tightrope, this fine line between what to give a reader and what I need to know as the author.  Give the reader enough information to care -- to show that even the "bad guy" isn't all bad, and the "good guy" has some issues to work out -- but not so much information that the story lags.  

And I know most of it before I start.  Maybe its because I write mysteries, but I feel like I need to at least know who the antagonist is before I write the first words of the story.  I couldn't imagine having my characters decide they needed to change their past on me!  YIKES!

But I do want to know.  Do you, as a reader, want to know their whole pasts?  Or just enough to make the story flow?  

Blessings!

Nichole