Argonian Necromancer you meet deep in the Olenveld sewers.

He is completely insane in his reasoning.

His dialogue:

Ah...the troublemaker of our cause. I am glad I have the chance to finally meet you.

--

You call our cause madness, I call it progression. I lost someone I loved with all my heart. The Black Worm made it possible to be reunited.

--

Just like her family... You do not approve of my decisions. Very well, you shall share the same fate then. I will enjoy killing you slowly...