Backstories are vital for good characters. If your character has no backstory, then they have no justification for their stats or basis upon which to act. Backstories are one of the important reasons why DnD is a RPG and not a War Game. That being said, creating a compelling backstory is not easy, especially not when there are so many character archetypes out there that make it seem like your ideas aren't original. Here are some tips for creating an interesting backstory without falling into boring clichés.
A backstory consists of two fundamental parts: Tragedy and Motivation
Now let's first talk about the first part and then we'll explain how it can inform the second.
Tragedy
Tragedy need not be severe. Let me say that one more time for the edgelords at the back: tragedy need not be severe. Yes having your parents both die is tragic, and there are some (many) incredibly compelling characters that are orphans. But A) this is now a bit of a cliché and if you're looking for originality this will take points off and B) this is pretty much the most tragic thing that can happen. Beyond having your entire family and group of friends or colony die, this is pretty bad. Hell, anyone close to your character dying is tragic. And once again, this is very much a viable tragedy, but is it a compelling one? Does it fit for your character's vibe? If you're playing a wisecracking jokester then horrendous tragedy might not be the way to go. Or maybe it is exactly the way to go, but do it so over the top that it in and of itself becomes comical. But for the moment let's think a little smaller. To a child, losing a toy is tragic. Missing out on a promotion is tragic, as is losing grandma's apple crumble recipe. Think about things that suck in every day life, and then ask yourself if, in a different world (like a fantasy one), would this be something that would drive you to drop everything and go on a quest? Boredom is tragic. Now, the smaller the tragedy the less easy it is to see how it drives motivation, so let's talk about that.
Motivation
The reason tragedy is a necessity is because it fuels motivation. That's why severe tragedies have clear and strong motivators. Thug killed your parents in an alleyway? Find thug and take vengeance, boom motivation. But riddle me this, what happens to your motivation after you've gotten vengeance? Do you hang up the cape and cowl or try to become a symbol that prevents others from losing their parents? This is the real challenge. What are the long term motivators of your character? Regardless of how severe your tragedy is, that is the question you need to answer. And oftentimes minor tragedies have just as compelling long-term motivators as severe tragedies. Take the boredom backstory. Your character grew up in a cushy home, had enough food, and had a stable job lined up. They thought this was boring and decided to go become an adventurer. Now what motivates them, both in the short and long term? Simple, finding adventure and experiencing the wildest things they can. This can explain so many different actions, and its always justified. Of course, maybe your character was just bored but you play them cautiously, this can explain it too, since they might realize that their life was boring but pleasant, and they would like to return to it at some point. Defining your motivation gives your actions justification and direction. Picking a tragedy makes defining your motivation easy.
Now Twist!
This is where, if you want, you can take the elements assembled and use them in counterintuitive ways. Take the opposite of the cliché motivation that goes along with that tragedy, or take it to the absolute extreme. Have a minor tragedy that's create an insane amount of motivation. Have a major tragedy that barely effected your character at all. Dang it do the exact opposite of exactly what's recommended here and build a character that has just gone along with whatever anyone around them has suggested, and committed to it 1000%. Novel backstories come from the unexpected, the misinterpreted, the illogical.
And just like that your backstory takes on a flair of its own. Now, ideally your backstory fits hand-in-glove with your stats, class and race. You should never forget your class and race when crafting a backstory, but you can make any backstory fit so long as you can justify it, and as we've said justification comes from interpretation. And once you've created a backstory, you get to make a whole new story: the story of your character from here on out.