Confession time: I love tragic backstories. The minute a character starts talking about his past and the angsty music starts playing I get chills up and down my spine and hug my knees in anticipation.
Backstory is important, and tragic backstory most of all. It's usually the sad, traumatic stuff that really changes a person and drives him on to a goal, whether it be revenge, closure, penance, peace... you name it.
But I'm not the only one who likes backstory, as evidenced by the surplus of tragic backstories cluttering up every angsty teen novel or movie. Let's face it: tragic backstories are now cliché. And that's a bit sad. But just because they're overdone doesn't mean you can't write one that's meaningful and original.
1. Does your character really need a tragic backstory? Sometimes your story will work fine without one. Sure, they're fun to put in and it's tempting to throw as much trauma at your main character as possible, but if it doesn't add anything to your story it's not going to impact your readers much. It's a pity to waste a good tragic backstory, so make sure it's doing its job.
2. Do the readers need to know what it is? Sometimes you can get away with simply hinting at tragedy in a character's past, without actually having to tell the readers what it was. You can't always get away with it though, so use discretion. (You don't want your readers doing this)
First let's look at some cliches. Most tragic backstories involve death of some sort—usually the character's family. While that's certainly sad, it's also overdone, meaning readers won't be as affected by it. It's not that modern-day readers are a cold-hearted species (well, maybe we are a little), it's just that if they've seen it too many times they don't care about it anymore.
Yet another cliché is putting the character through unspeakable tortures (usually perpetrated by his arch-enemy). Personally I like this one a lot but *sigh* it's overused.
(Oh, and don't make his planet get destroyed. That's also overused.)
A tragic backstory doesn't have to involve the death of a loved one. In Herman Melville's short story “Bartleby the Scrivener” the main character's tragic backstory is simply that he worked for years in the Dead Letter Office (where letters go whose addressees don't exist or are dead). Going through all that mail for people who would never receive it so thoroughly depressed him that he was unable to function in society. It's an unusual backstory and because it's unusual, it gets readers' attention and makes them wonder, “what would I be like if that had happened to me?”
A tragic backstory doesn't have to involve death at all. In one of my stories I originally planned to kill off the protagonist's father as part of the catalyst, but I later decided to make the government take the protagonist away from his father instead. It wasn't quite as sad, but I wanted the boy to have the bitterness and sense of injustice that the latter option afforded. (Oh, and it wasn't quite as cliché, either.)
A tragic backstory doesn't have to be something big. In Les Miserables the protagonist, Jean Valjean, has a backstory of many years spent in prison. But this isn't his tragic backstory. Sure, it's tragic, but it's not what's at the root of the decisions he makes through the rest of the story. What really changes his outlook is when he robs a little kid—and right after someone's been kind to him for the first time. Tragic backstory isn't always someone doing something bad to you; sometimes it's you doing something bad to someone else. Wrongdoing can be terribly painful because you can never go back and undo it no matter how much you may want to.
In all of these examples there is an important truth involved:
What happens is not as important as what it does to your character.
In The Man Who Was Thursday by G. K. Chesterton, the protagonist witnesses an anarchist's bomb go off in the street, killing several people. This incident, even though it didn't touch him personally, gives him a hatred of anarchy and a love of law and order that eventually leads him to join the police force. His backstory is a major motivation for his almost religious zeal in fighting anarchy.
Many cliché backstories—loved ones dying or the character getting tortured/maimed/scarred—have no other purpose in the story except to make the character seem more “tough” or “cool”. That's part of the reason why these cliches don't affect readers like they're supposed to. Our own tragedies don't make us feel “cool”. Backstory must serve a purpose beyond simply impressing readers; it must give us a window into the character's heart and mind—how he sees this event, not how we see it.
After all, what makes the event tragic is its affect on the character. Killing off your character's family won't hurt him much if he didn't like his family to begin with. Some things (like Jean Valjean stealing a coin from a little kid) won't affect some people but it will have a huge effect on others.
I'm not completely against killing off your character's father/wife/child/uncle. Or against giving him a tragic, abused childhood (another cliche). But you don't have to go with what a million other people have already thought of. Many people (myself included) don't have tragic pasts, but everybody has had things happen that he didn't like and that changed the way he looked at the world. Dig into your own past and find some of those things.
Those are the things that make people cry.