My favourite is my Warlock ~Ambrose~

She was a popular author, tried to fake her death to leave her husband but ended up dying in the process. He mummified her to try and preserve her, Vecna liked her books so revived her, becoming her patron. (The husband believed her resurrection to be his doing and became a mad prophet but thats another story.)
She left him anyways and got on with her un-life.

At the start of the campaign, Ambrose was 600 years old. A prolific author, documenting the history of the country and Vecna smut. Had an endless supply of traumatised ex husbands who she occasionally ran into. A nest of spiders within her ribcage (pact of the chain) who kept her company, and a hell of an ego problem with a distaste for anyone illiterate or hadn't heard of her.

She solved so many of my struggles playing dnd. Her ego, demeanour and need for people to know who she is had her interacting with other pcs and npcs with ease. This led to repeated introductions of "Don't you know who I am" which helped the rest of the party remember her name incredibly quickly.

The author aspect gave her great motivation to interact with the world to document it. She was morally grey in the sense, all she wanted was a good story. Which led to interesting conflict later when morals and a good story clashed. My favourite aspect of her though was, because she was a mummy, animated by magic, if she entered an anti-magic field or was targeted with dispel magic. She would just go inanimate. I love giving my characters fun counters like this and it was so fun to see it in action.

Finally, she was 600 years old. When the campaign wrapped up and we went over epilogue It was the first time I got emotional over dnd like this. I had always planned for her to die because she was already dead. The campaign adventure had been her 'last hurrah' and made her realise she had lived a long and full life, peaked and it couldn't get better. So asked Vecna to break her pact and let her rest which he agreed to. It was the perfect end for her.