Shadow, Wolverine, Boba Fett. Everyone has their favorite antihero or villain with a mysterious backstory. They are rugged, independent, pay lip service to the law, and don’t play well with others. Basically, they are everything a social outcast, (i.e. a nerd, before it was cool), from a country of pioneers that revolted against the motherland would want to be. While their mysterious past is rarely the main appeal of such a character, it certainly is a key part of what makes them interesting.
It would perhaps be wrong to say people love mystery or they love to solve puzzles. Rather, people have a need to figure things out, an urge to find some kind of resolution. The desire is so strong that it compels them to create the missing pieces of the puzzle, or it drives them insane. For evidence of this, look up some of the theories about the secret meanings of Don Quixote.
This compulsion has the unfortunate tendency to ruin characters for whom mystery is part of their allure. When Shadow, from Final Fantasy Six, is first introduced, we are informed that “he’d slit his mama’s throat for a nickel,” and “He owe allegiance to no one, and will do anything for money. He comes and goes like the wind.” If one finishes the game without learning his backstory, they are left with little beyond this initial impression, and the less said, the better. It allows the player to imagine a vague backstory as they will while focusing on the core of Shadow’s character, his awesome ninja skills and killiness.
When the player learns Shadow’s backstory, he ceases to be this ruthless badass with some vague past and becomes a guy who robbed a train, fathered Relm and then ran from his guilt over abandoning his partner in crime. He moves from being an awesome, killy ninja assassin guy to a man fleeing from his past, which detracts from his characterization as a badass. It leaves the player with a vaguely unsatisfied feeling when Shadow’s background fails to live up to the nebulous backstory they have constructed for him. The same is true for Wolverine, Boba Fett, or any other character antihero or villain with a mysterious past.
So, let’s leave the background of the badass, independent guy alone. It’s better that way, unless you want him to turn out to be a clone, or a depressed train robber, or a farmer from Canada.