The History is the most important aspect of your character. It is more important than attributes, more important than skills and spells, more important than any equipment. Why, you ask? Simple: it is the history that gives your character a meaning, a life of its own.
Darkening Sun is first and foremost a roleplaying mud where players pretend to be characters living in a realm of fantasy. To understand how your character thinks, acts with others and lives out his life you must know who he is, know the facts that made him that way.
A history does not have to be long, though a one paragraph history will hardly say much about your character. A history should be as long as you think is necessary to describe your character's way of thinking. And that is as important to you as it is to us.