Sheogorath, Prince of Madness.
He's irrational, emotional, hysterical. He is and was and will be feared by all, including his fellows in the daedric pantheon.
Change, war, love, hate, knowledge, virtue, trust, betrayal. These are some of the aspects of the daedric princes. All of these things are but products of the mind. We are all of us prisoners of the mind. Reality is a more subjective, more mailable thing than many people suspect. The demented reality that plagues a lunatic is as valid, if not more-so, than that which is supposedly shared by sane men.
In a very real way our perception is the world around us.
The mind is Sheogorath's realm. Emotion, perception. He can control the lense through which our reality is filtered. He can control how we perceive the world and those around us. Can inspire one. Can hurl another into a black depression. He can make madmen into visionaries and scholars into fools.
Music and murder, poetry and savagery, harmony and chaos. He can inspire all of these things or none of them. On a whim as unpredictable as tomorrow's winds. He doesn't have to kill you bodily; any lowly thug can do that. He can fundamentally change the most important part of you. The thing that makes you you. Your mind.
The only mitigating factor to Sheogorath's impressive and frankly frightening powers is that he is, by his divergent nature, incapable of having an agenda. He can not use his powers to bend the mortal world to his whim, because at any moment his whims can and will change.