Zellix is the founder of the Asylum run by the Society of Brilliance
Zellix is a cold, calculating mind flayer, but he only comes off as such because his expressions are hard to read. He is the head researcher on Madness for the Society of Brilliance.
Zellix was a mind flayer who founded and managed an asylum in the Underdark. Zellix discovered that brains of people infected by madness were more succulent and tasty than others. So it founded an asylum where it could keep them. If a patient was not treatable, Zellix indulged in their brains after humanely killing the patient with an injected serum.