The goddess of Harmony.
Cosmos is the Goddess of Harmony who opposes Chaos, God of Discord. Before Dissidia: Final Fantasy takes place, Cosmos and Chaos fought once before. Cosmos was unable to unite the power of the Crystals and was defeated by Chaos. Her power is taken from her in the form of the 10 crystals. She summons the heroes in an attempt to restore balance to the world and regain her powers.
She is a rather kind deity, and sees great remorse in her more wrong-thought actions.
She uses magic based-attacks, but can mostly only support her Warriors. Such examples, being when she gave her Warrior the crystals.
She can launch several lights orbs at once, cure allies, and use other supportive magic.
In the series' backstory, Cosmos was originally a manikin. But unlike the others, she was the only known successful specimen to have the full memories of a single person: Cid's wife. However, the Lufenians used her as an alternative means to soothe Chaos. After ending up in World B, Cosmos ruled the world alongside Chaos before Garland appeared to begin the conflict for Cid to oversee the powers of Harmony and Discord at their fullest.
During one of the earliest cycles, Prishe introduces Cosmos to the Warrior of Light another perfect manikin modeled after Cid, an individual that neither god summoned. While Cosmos was initially reluctant, she eventually imbued him with her light to serve as one of her champions. It was hinted that she was aware of the Warrior's true nature, as well as Prishe's name for him.