Lost Fans: Which Characters Had The Most Interesting Flash Backs?

In my opinon, it's got to be Ben Linus first (im a Ben Linus fan, mind me). I just think he's got one of the most interesting backgrounds of all the characters on the show, and I really enjoyed learning about what his childhood was like and the events that happened to him while growing up. Second it would have to be Richard Alpert. I mean, who knew he was THAT old :P? It was so interesting to see how he got on the island and how he became immortal. Then after him, it would be Smokie and Jacob, then Jack, then Kate, then Sawyer, then Charlie, then Juliet......damn it, most of them have interesting backgrounds! But i shan't name them all here XD.