Typically, characters usually have certain backstories to drop them into the plot and to make them who they are today, so to simultaneously drop them into and make them relevant to the plot based on their actions (usually in relation to our main character) -- at least that's how I see them. But how exactly would I write characters their backstories and make them all be relevant to points much later in the plot than when they were introduced to the audience and make it seem like it occurs naturally? Types of relevance I like is when something that seems somewhat unrelated to the overarching plot in their backstory, regardless of how small or big the occurrence actually is, actually becomes a crucial plot-point. Of course, also having a certain occurrences come back and influence the main plot is also important. Basically, what I'm asking is: How would I write a backstory that isn't just there to give one character reason to exist or be what they are, but also be something that enriches the plot and the world for the audience? Making potentially subtle (or more pronounced) connections between two previously seemingly discrete backstories? Follow-up: How would I write a tragic backstory and also make it relevant to the plot like I asked above? And if I were to want to make multiple characters have some form of bad history, for, say, a particular genre (melding Fantasy and Psychological Thriller, for example) how many is too many? Making potentially subtle (or more pronounced) connections between two previously seemingly discrete backstories?