They are "wicked, bad, false, untrue, the originators of mischief, most baneful, destructive, the basest of all beings." The whole universe is full of them.

They aim primarily at destroying all the good creations of Ahura-mazda; but if unable to destroy they content themselves with perverting and corrupting.

They dog the steps of men, tempting them to sin; and, as soon as sin, obtaining a fearful power over them.
At the head of Ahura-mazda's army is the angel Sraosha (Serosh).

Serosh is "the sincere, the beautiful, the victorious, the true, the master of truth." He protects the territories of the Iranians, wounds, and sometimes even slays the demons, and is engaged in a perpetual struggle against them, never slumbering night or day, but guarding the world with his drawn sword, more particularly after sunset, when the demons have the greatest power.
Angro-mainyus appears not to possess any such general-in-chief.

Besides the six councillors above mentioned, there are indeed various demons of importance, as Drukhs, "destruction;" Aeshemo, "rapine;" Daivis, "deceit;" Driwis, "poverty," etc.; but no one of these seems to occupy a parallel place in the evil world to that which is assigned to Serosh in the good.