Ægis, Greek mythology.
The goatskin breastplate or shield of Zeus(King of the gods) or
Athena (goddess of wisdom). The shield, Ægis, when carried by
Athena has the
head of Medusa, retaining its powers of petrification, attached to the center.
The shield offered protection and security - to be under the ægis of someone, or something, is to be under its protection.