sgamadison asked me to ask Joe this question: "Since very little of Sheppard's background was revealed until Outcast in season 4, did you create your own backstory, and what was it?"
He said that starting in season 1 he did create a backstory, but when he realized "they" didn't care, he "tucked it away in a secret little place up here" (pointed to his head) and there it stayed. He felt they could have explored his character a lot more, and Outcast was written to do that.
David then said that the writers realized they'd plumbed the depths of that character, and that there wasn't much there ;-)
He also said that McKay already had a backstory, they just had to figure out WHY [he was that way!]
Photo of the 2 of them taken while I was waiting to ask my question. It's not a great photo, since it was taken with my little point & shoot camera, but it *is* from the question line :-)
[edited to unlock :-)]