The prisoners name is Valen Dreth. I had a lot of fun with him in my fan fic, using him as the principal villain in two chapters. The following was Teresa's first meeting with him:
"You!" A distinctly elven voice brought her head up to see an ashen-skinned Dunmer striding toward her. "It's you! I know it!"
Out of habit, Teresa's eyes darted from one side to the other. There were crates piled up to her right, blocking any escape. But the way to the left was open…
"You thought you could trick me did you!" The dark elf exclaimed, and Teresa bolted. She had no idea who the Dunmer was, or what he wanted, and was not about to wait around to find out. She heard feet slapping on the cobblestones behind her, and darted into the first alley that cut through the insula wall.
Hard fingers clamped down around the neck of her rough tunic, and the young Bosmer was jerked to a sudden halt. Gasping for breath as the sackcloth dug into her throat, she vainly clawed at the hand that held her in place. Yet she could not reach back far enough to reach it. Then a moment later she felt another powerful mitt grasp a handful of her hair and shove her into the stone wall of the alley.
Stars danced before her eyes as her skull bounced off the unyielding rock. When the world swam back into view, the dark form of the Dunmer loomed over her, eyes glowing like red pools of fire. But it was the silvery glint of bared steel that caught the child's gaze. The long, slender blade glittered as it hovered above her face, just inches from her pale skin. Teresa felt warm liquid spread down from her waist as she waited for it to sink into her flesh.
"You had better piss yourself you little Witch!" the Dunmer hissed like an angry serpent. "Don't think that I don't know what you're up to."
"Please sir," Teresa blurted out, trying to sound as innocent and helpless as possible. "I didn't do anything! I'm just a kid!"
"Oh, that's what you all want us to think, isn't it?" Teresa's emerald eyes were fixed upon the hard blade of the knife as it moved back and forth in front of her face. "Just a little girl is it? Only a child? You may have fooled the rest of them with your foul sorcery, but not Valen Dreth! I can see through you, all of you!"
"I don't know what-" the wood elf was cut off as the man's free hand wrapped around her throat and clamped down hard. Her eyes bulged from their sockets as she fought for air, and her hands pulled against his own. Yet he seemed made of iron, and she nothing but chaff. There was no relenting of his death grip.
"Don't try to lie to me!" the ashen-skinned man's voice was loud as thunder in Teresa's ears. "I know you cursed me! That's why every gladiator I bet on loses! It's all your fault, yours! You Witches have always had it in for me, but I know how to deal with you!"
"What's going on back there?" The low growl came from the mouth of the alley. In an instant the iron bands of the Dunmer's fingers disappeared from Teresa's throat, and the glittering steel of his blade vanished into one of his flaxen sleeves. He took a moment to smile at Teresa, and the little wood elf imagined that was how a slaughterfish looked when it bared its teeth. Then he turned to face the Imperial Legionary standing behind him.
"Oh nothing." Now the dark elf's voice was smooth and carefree, like a playful wind on a cool Spring day. His hand dipped into a pocket, and darted forth like quicksilver a moment later to toss a copper reman at Teresa. "I was just doing my part to help this poor unfortunate here, praise merciful Stendarr."