Proxies are those beings - primes, planars, and even petitioners - specially chosen to act as agents of the powers. Usually, the body chosen is transformed into a creature favored by the deity - into an evil rutterkin or a good deva, for example. On rare occasions, the being isn’t transformed, but is bestowed with special powers.
Proxies are absolute servants, obeying the wishes of their deity as fully as is appropriate to that alignment. Those of good powers are unswervingly loyal and obedient, and those of evil powers are utterly difficult and tricky, even for their masters. On the Upper Planes, a proxy knows he can rise even higher through good service. On the Lower Planes, a proxy usually prospers by finding some clever and nasty way to create an opening for his high-up man.
Note: Proxies originally appeared in this form in the Planescape AD&D campaign setting from TSR. Their use here is for the purposes of providing context for the campaign only.