Demodand

Demodands, also called deodands or gehreleths, are a race of Neutral Evil fiends who were exiled to Carceri long ago and are its self-appointed jailors.

Demodands are, pound for pound, some of the strongest fiends in Planescape. They're far less numerous than the baatezu, tanar'ri, hordlings, etc., but in a one-on-one, demodands are stronger than almost all of them.