What To Do When You Realize You Don't Know Your Main Character Like At All

I just realized as I was preparing to write an entry about Dante, my MC, that I don't know him, like at all. Which scares the hell out of me because I've been writing him for more than a year. And I barely know anything past his basic info: Name, Date of Birth, Blood Type, etc., but other than that, I don't really know too much about him. I do know his personality a bit, but like I said, it's not a whole lot. So what I'm gonna do is head up to the store and buy a huge 5 subject notebook like I did for the other story I'm plotting for next year's NaNoWriMo (or this year's, I guess you could say now) and start writing down everything I can. The other thing I did for this story is use binder clips to clip each section together. Like for instance, I have a bunch of stuff about the main character Danya, so for all his stuff, I use a blue binder clip. And for plot stuff, I have a yellow binder clip. And for another main character's info I have a green binder clip. It's really hard to explain. But it works beautifully. So tomorrow I have to go up to the store and get another 5-subject notebook plus small binder clips that I can use to organize everything. Fun fun.