"Necromancy isn't illegal when its done to humans and beasts. I'd never desecrate a Dunmer that way!"

Strangely enough, the town guards don't listen to my necromancer's protests. He's a Dunmer, a former slaver for House Dres who traveled to Elsweyr in hopes of finding some Khajiit laborers who want to emigrate to Vvardenfell. He's not having much luck with that, and that was before the dragons showed up...

I used the maormer skin with a dunmer oracle eyes approach. Made him a tribal shaman looking sea elf. Taught necromancy by the sload. Would be a waste not to take use of all the dead the ocean provides.

I generally have trouble with even window dressing backstories in MMORPGs. Only one character (a minor one in my interest/play list) ever had the outlines of an identity suggest itself - the necromancer I made for the Elsweyr drop. Laelia Annaeus. I think this is because she is an Imperial sometimes taken for a Redguard (this was suggested by her appearance, which was fun to make). She identifies however as Imperial (since that was what I chose under race selection). Given this, it's easy to imagine a bit of potential personality. Raised and trained in Cyrodiil, she favors that part of her heritage. She's an Imperial's Imperial, inspired by her friends and family. She entered Imperial service with the goal of rising as far as possible.

Then the Emperor disappeared and necromancers started showing up. Following her ambition and curiosity, she went along with the changes - to play the game with the new rules. Knowledge is power, and you have to be in the game to see the board. This angle avoids the "she was forced" angle wherein she had to play along solely to survive. That was true, but she was also motivated to continue climbing the ladder of success and to arm herself with power and knowledge that would give her an advantage no matter how things played out. This gives the character more agency than excuses.

At this point however, the fuzzy image that popped into my head of who this character is less clear after that. Two possibilities suggested themselves:

The first (no favorites, random order) is that she would have continued her rise in power in the Worm-riddled Imperial government and military if she hadn't been betrayed by another ambitious individual. This lead to her arrest and her execution as a sacrifice to Molag Bal. Arriving back on Nirn, she decided that High King Emeric and his Daggerfall Covenant was the best bet for the Empire she knew to be restored. Besides, she still has relatives in Alik'r, even though she isn't close to them. She still has the same goals, only now she will help drive out the Daedric forces and position herself to be a key figure in the restoration of the Empire. This version of the character would likely be a tank, leading troops into the heat of battle, or a fierce damage dealer removing an obstacles to the future she is willing into being. She isn't worried about accumulating or dwelling on regrets or hesitating to restoring and being a new architect of the Empire. The faster she can help end the war, the better. If using undead as fodder on the battlefield means fewer casualties among the living and a quicker resolution to the Three Banners war, so be it.

The second is that while learning and practicing some basic principals of Necromancy, she gained some profound insight into the workings of life - the cycle of birth and death, of growth and decay, of decline and renewal. Not as grand as mystical vision sent by the gods, not as mundane as logical conclusion to a series of logical propositions, it was more of an intuitive realization and awareness resonating with her heart and mind. As each spellcaster brings their own personality and desires into their magic, their exploration and discoveries can follow unique lines. This intuitive awareness suggested that even the cosmos itself operated on the same principles, and that the stereotypical use of necromantic magic is a foul pittance of the greater potential. Yet everyone seems locked into a quick and dirty power-grab kind of use, hence to gateway to greater things still lies in mastering those lesser spells first. And survival as well. This version of the character would likely be in a healer/support role, looking to explore and utilize her powers for more than just violence and intimidation. A vision of an Empire healed and elevated beyond what most could dream of by the wisdom and insights she has glimpsed drives her forward.

The second version would have an especially intrigued view of Vastarie, for example, while the first would have a great deal of respect and empathy for Abnur Tharn.

Oh I guess I might as well answer the original question.

My Dunmer stam necro is an ace treasure hunter who became desensitized to undeath during her decades of dungeon delving, and ultimately turned to using the dead for backup to keep herself alive. The Worm Cult tried to recruit her, but when she turned them down they decided to just harvest her soul instead.

My Breton mag necro was a member of the Worm Cult, but was considered expendable enough to be used as a sacrifice. She has a very pragmatic (and slightly sociopathic) view of her trade, and considers both the living and the dead to be little more than tools. Now that the Cult has cut her loose, she's free to pursue her own goals, and she really doesn't care what anybody thinks of her preferred methods.