Not much is known about Kakashi's past, except that he lost his best freind and all those he loved a long time ago.

Kakashi grew up in a time of war, much like Naruto, Sasuke, and Sakura, except at a much younger age. He harbors a lot of guilt of what happened during the time, and it's apparent that he lost a great deal of friends at the time. In most probability, his entire team with the exception of the fourth.

And lastly, in addtion to Kakashi's angsty past, he los tthe fourth which was his teacher and idle. He is the only jounin in the manga so far that has had a teacher die at such a young age. This is probably when he started to idolize Jiraiya. Well, not idolize, but he seems awfully found of him. He also is one of the only people in the manga so far to have outlived everyone of his freinds and family, and he seems to be very concerned about the lives of others. (of course, it seems like he's still concerned about his life, but probably less than when he was younger.)