A few days ago, I had this idea for an NPC.  She is a fantasy interpretation of Saint Lucia of Syracuse, that has been heavily influenced by the Dante's Inferno incarnation of her character.

Her backstory is dark and twisted, full of abusers and defilers. She has suffered, more than any mortal should ever have to suffer, and that suffering has turned her into a Paladin of Vengeance.

While discussing this NPC on Reddit, lots of people pointed out that she is an OP edgelord of cringe, and this got me thinking.

How do you play characters or NPC's who have horrible, dark, twisted backstories that make the other players shudder, without them becoming a lord of cringe?

Also, as a DM, how do you play extremely powerful NPCs, without them seeming OP, and should you even try?

So guys and girls and beyonders.  Copper for your thoughts!

One of the defining traits of cringe-y characters for the edgelord flavor is the fact that they are always brooding, looking people with disdain or contempt for their ignorance of how dark and horrible the world really is, and most often than not all too ready to tell everyone of their tragic past, how they suffered, how they are really-really angry all the time, how powerful they are due to their suffering etc.

Just... don't play them like that.
Someone who suffered a lot will most probably not be too fond of sharing their experiences with anyone they do not know and trust, especially if they are still hurting or have been too deeply changed by these experiences. Rather than being suspicious of everyone and everything and being angry all the time, they would most probably just try to avoid unnecessary contact with anyone, but it's not like they are completely antisocial and incapable of basic social interaction.
They would also most probably not consider themselves powerful, as people who suffered a lot usually feel small and weak, unless they somehow got over their suffering, therefore they would not do much unless inevitable. The fact that they might indeed be extremely powerful should only be important when there is no other option but for them to step in and do something but they should otherwise try to avoid conflict.

The  edgelord character "can" work in a "solo" story (see Berserk for a prime example), but for an RPG with multiple "main characters" (the PCs) it is usually counter-productive, as introducing an extremely powerful character who is clearly and always more powerful than them takes away from the centrality the PCs usually need to have in order for the game to be fun, and might make players thing "Man, why doesn't this person does everything then, if they are so powerful? What are we even doing here?", especially if the NPC in question is not showing any kind of restrain or doubt in their actions.

I feel it is also usually a matter of how they are presented visually that defines them as edgelords, so better avoid spikes, black equipment all over the place (unless that's something they are famous for in the game world for some reason or another), particularly impressive and "dark-themed" weapons or armor and the like.

There is a very fine line between "troubled-yet-interesting-and-useful" NPC and "cringelord", one that is not really easy to run on.

Disclaimer: the above is obviously just my opinion, I do not expect anyone to agree by default.

Some of LeK's descriptions remind me of an old text-ish adventure called Leather Goddess of Phobos.

Now, I can't stop thinking about edgelords of cringe (a phrase I've learned ITT) in the same flavor Dr. Frankenfurter. 🤣

"Troubled-yet-silly" NPC and not cringelord.

I think Lek made some great points. As awesome and dark as your NPC's backstory may be, try to avoid ramming it down your player's throats. They can tease her backstory out of her bit by bit as the story progresses, with occasional help from you to move things along. I think a little bit of mystique can go a long way in encouraging that sort of dialogue between your players and NPC as well. Allowing them to grow attached to this character before knowing her dark history in all it's detailed "glory" might even make it more dramatic. Granted, I've never DM'd a session in my life and I could be way off!

No other answer than 'depends'.  Some might be consumed by their tragedies, some may say :Well, that's in the past" and move on with their lives, most probably somewhere in the middle.

My most tragic character was a Shadow Sorcerer was abandoned as a baby in the trash, taken in by a lovely couple who sheltered him when realising how strange he was and then his powers made him accidentally kill a puppy and they began to fear him. When his powers escalated his mother killed him and they buried him in the garden. Yet, having a soul literally bound to the realm of shadow and death, he didn't fully die and came back to life where he ran away. He lived on the streets struggling to survive. He was taken in by a sorcerer noble, who taught him to use his magic and lived an ok life until this "new mother" died of illness. So off he went on adventure. Then he drowned. Then he came back. 

Normally would be ultimate cringe edgelord except he was actually an upbeat person, optimistic and a bit of a prankster. His feeling was, shit happens, life is weird, not worth moping about so get the feck on with it and live your life the best you can. 

He was great, until a TPK ended the campaign and we began another.

Much like Cyb3rMind, I play a Shadow sorcerer with a tragic past that is also a Fallen Aasimar. But he's an upbeat kid that always tries to find the silver lining in things.  Despite never talking about his past, always smiling, and being generally pleasant, any time he uses his Shadow powers or Aasimar's Necrotic Shroud ability, I get jokes from everyone else about being the edgelord goth kid.

My point is that it is an internet stigma that can't really be escaped. Play the character (or NPC) true to your concept and let everyone else worry about how they view it.