During the episode "Captain Jack Harkness" Toshiko asks Jack who he was before he took the Captain's name. Jack looks confused and doesn't answer. This is my explaination of his non-answer. It's a little short, but I didn't really quite know anyother way to end it.
Disclaimer: I don't own Torchwood, it is the right of his respective owners.
"Who were you before you took his name?"
Jack didn't know how to answer. A con-man? A murderer? A nobody? How do you tell someone that your memories are so far down, so repressed, you can't even remember having them in the first place? Toshiko wouldn't understand. Hell, he himself didn't understand most of the time. Who exactly was he?
He certainly wasn't Captain Jack Harkness. That man was a hero who sacrificed himself for his men. But Jack; Torchwood Jack, Time Agent Jack, Unable-to-die Jack; well he was not a hero. He was about as far from hero as a person can get.
"Who were you before you took his name?"
I wish I knew Toshiko, I wish I knew.