An angel is a celestial agent sent forth into the planes to further its god's agenda for weal or woe. Its sublime beauty and presence can drive awestruck onlookers to their knees. Yet angels are destroyers too, and their appearance portends doom as often as it signals hope.
An angel's moral compass grants it a sense of infallibility that can sometimes spell its undoing. Angels are usually too wise to fall for a simple deception, but sometimes pride can lead one to commit an evil act. Whether intentional or accidental, such an act is a permanent stain that marks the angel as an outcast.
Fallen angels retain their power but lose their connection to the deities from which they were made. Most fallen angels take their banishment personally, rebelling against the powers they served by seeking rulership over a section of the Abyss or a place among other fallen in the hierarchy of the Nine Hells. Zariel, the ruler of the first layer of the Nine Hells, is such a creature. Rather than rebel, some fallen angels resign themselves to an isolated existence on the Material Plane, living in disguise as simple hermits. If they are redeemed, they can become powerful allies dedicated to justice and compassionate service.
An angel doesn't require food, drink, or sleep.