Zehir is the evil god of darkness, poison, and assassins. Snakes are his favored creation, and the yuan-ti revere him above all other gods, offering sacrifice to him in pits full of writhing serpents. He urges his followers to:
Hide under the cloak of night, that your deeds might be kept in secret.
Kill in Zehir’s name and offer each murder as a sacrifice.
Delight in poison, and surround yourself with snakes.