Penthesilea is a character from greek mythology. She is daughter of Ares, sister to Hippolyta, Antiope and Melanippe, and founder of the Amazons.
The details surrounding Penthesilea are not very clear, but it is assumed that like her Amazon sisters, she was born when the Greek Goddesses threw the souls of women murdered by men into the Aegean Sea where the souls formed with the clay at the bottom then rose to the surface giving birth to the Amazons. Since then she has served under her sister Queen Hippolyta.
In Persona 3 Penthesilea is the persona of Mitsuru Kirijo.