Description

Aegis is an android, an Anti-Shadow Suppression Weapon, sent to observe the protagonist and a member of the Shadow Operatives along Mitsuru and Akihiko. When she was first encountered in Persona 3 and after joining SEES, Aegis operated truly like a robot: her initial personality was simply to obey orders. Due to her humanoid appearance, it allows her to process thoughts like a human, which in turn makes it easier for her to handle a Persona.

After awakening to the Wild Card, Aegis' personality further develops into her current personality of a sweet, gentle, empathetic and strong-hearted young woman with a talent for leadership. She is also very polite to everybody, always using the suffix '-san' when addressing them. In the original Japanese version, she ends her sentences with "de arimasu" prior to developing emotions.

[Edited from Megami Tensei Wiki]

While she can wield multiple personas, she's most commonly seen with Athena, the Greek goddess of justice, wisdom and warfare.