Fiend

A fiend was an evil creature from one of the Fiendish Planes. They are not just evil, but born of Evil; primal malevolence is one of the roots of their nature, and the evil essence of the fiendish planes permeates every part of their bodies.

Demons
Demons were chaotic evil fiends, native to the Abyss. Tanar'ri were the dominant species of demon, but there were a number of others.

Devils
Devils were lawful evil in alignment and hailed from the Nine Hells of Baator. The baatezu were the dominant species.

Yugoloths
Also known as daemons, yugoloths were neutral evil in alignment and inhabited the Blood Rift.

Demodands
Also known as gehreleths, demodands were said to have been fashioned by one of the primal creations of Evil, exiled because of their chaotic taint. They dwelt in the Supreme Throne.

Relations
The tanar'ri and the baatezu held an eternal enmity for one another as they waged the Blood War.