So my first character was a Paladin, my favourite characters to play USED to be noble knights in shining armor. But my favourite character to date went in the complete opposite direction. Meet Amelia, on paper she is a Simic Hybrid Barbarian. For those unaware, a Simic Hybrid is from the Guildmaster's Guide to Ravnica, and is basically a human(oid) with certain augments or mutations based around different animals, like crab claws and the ability to climb.
This was a homebrew world, so there wasn't a good explanation for her large claws and gliding fins, unless you have a bit of an imagination. Amelia used to be a beautiful noblewoman, sought after by many suitors and would have eventually been married off, probably for a sizable dowry or the like. But one day she was kidnapped from her home and subject to horrible experimentation. The result was a thin woman with massive demonic arms attached about midway down her torso.
When the party found her, she had just escaped the place where she was being worked on, and she was terrified. Monsters around her, she panicked and was sure she was going to die, until something inside her took over and proceeded to kill the monsters violently.
This something was a demon, namely a Molydeus who was fused with Amelia, and they were stuck together. And so some time went on with Amelia terrified of the creature inside of her, and while she needed to rely on him for fights, she could not let him have free reign. But their relationship was predatory, with Amelia being pushed around constantly and almost always at the Molydeus' whim. Until finally the demon pushes Amelia too far, and she ends up having a conversation with him face to face, Naruto style. She makes it very clear that she knows he's a prisoner inside of her, and it doesn't have to be that way. She wants to help him accomplish what goals he might want to within reason, as partners. But no more of this bullying crap, this was her body still.
From that point on, the Molydeus named Zariah respected Amelia. Life went on as usual, Amelia ended up joining the same guild that the party was from, and ended up having a friendly relationship with the guildmaster, who was completely unapproachable to most. Amelia tended not to fear most things after a certain point, since she has a demon living inside of her and things don't get much worse than that.
A lot of her arc came from her trying to figure out who she was. While she was in control of her body full time, it didn't stop the demon from trying to influence her. Following the death of a party member and friend thanks to the Bard getting charmed by a Rakshasa, she came very close to killing said Bard in her rage and grief, but at the last second managed to stop herself. After this incident, whether or not Amelia was truly in control was a heavily debated topic, that had no clear resolution for a while.
During a quest to restore the sorcerer's age after a Wild Magic incident, the party went to a town that was governed by angels. As you can imagine, a human very much touched by a demon attracted their attention. After a tense roleplaying scene, Amelia declared to the angels and to the party once and for all that she is the one in control, not the demon, and that inside she is still human. This was her motif for a while, no matter what she looked like she was still human.
So imagine the shock when sometime later she is told that this is incorrect. I believe it is a mage who ends up revealing to Amelia that her soul is no longer entirely human. The experimentation to fuse her with Zariah fused not just their bodies, but their souls. One cannot exist without the other, and fundamentally Amelia is no longer human. This crushes her for some time, and she goes through what can only be described as an existential crisis.
Eventually though, Amelia decides that there is no point in wallowing over her situation, she needed to accept what had happened and move on, even if it is as a demon. And this revelation frees Amelia from her struggle since the beginning of the campaign. It didn't matter what she had become, all that mattered is what she did now. This began Amelia's transformation from the reluctant noblewoman to a complete and utter badass, whose goal was to hunt down devils since that is what Zariah wanted to do. And since the Rakshasa who killed Amelia's friend before was also a devil, she had no issue with this.
And once Amelia finally stopped questioning who she was, she had a very unique outlook on good and evil. The gods were just as cruel as demons and devils sometimes, and really good and evil comes down to perspective. She grew to be a very opinionated person, she disliked cowardice and highly valued loyalty. She wasn't an evil character despite her demonic power though, but this didn't stop her from doing what needed to be done. When one of the characters' father sent goons to drag her back home, Amelia used herself as a decoy with an illusion and threatened to send him back to their employer in pieces. She was fiercely loyal and someone you really wanted to have on your side, and someone you don't want to meet in battle.
She was my introduction to playing a character that wasn't a goody two-shoes, and she is my favourite character to date.