Namtar

Namtar is the son of and messenger for Ereshkigal, a goddess of death. He usually takes the form of a large, intimidating serpent. He is a fierce, vengeful deity whose domain includes disease, poison, and pestilence. The Allatu believe that he delivers disease to those who displease Ereshkigal.
Additionally, when Ereshkigal designates a mortal who will carry out her will, Namtar serves as their guide and mentor. He usually appears in their dreams, though not always in serpent form. Sometimes he can also speak to them in their waking hours as a whispering, sibilant voice. 
Namtar is often a difficult mentor, as he does not understand the hesitations mortals have around violence. As far as he is concerned, anything done in the name of Ereshkigal is justified.