The Morrígan is a goddess of battle, strife, and fertility. Her name translates as “Phantom Queen”, which is entirely appropriate for Her. The Morrígan appears as both a single goddess and a trio of goddesses, which includes the Badb “Vulture” and Nemain “Frenzy”. The Morrígan frequently appears in the ornithological guise of a hooded crow. She is one of the Tuatha De Danann “People of the Goddess Danu” and she helped defeat the Firbolgs at the First Battle of Magh Tuireadh and the Fomorii at the Second Battle of Mag Tured.
By some accounts, She is the consort of the Dagda, while the Badb and Nemain are sometimes listed as consorts of Néit, an obscure war god who is possibly Nuada the Sky Father in his warrior aspect. It is interesting to note that another battle goddess, Macha, is also associated with Nuada.
The origins of the Morrígan seem to reach directly back to the megalithic cult of the Mothers. The Mothers “Matrones, Idises, Dísir, etc.” usually appeared as triple goddesses and their cult was expressed through both battle ecstasy and regenerative ecstasy. Later Celtic goddesses of sovereignty, such as the trio of Éire, Banba, and Fótla, also use magic in warfare. "Influence in the sphere of warfare, but by means of magic and incantation rather than through physical strength, is common to these beings."
Éire, a goddess connected to the land in a fashion reminiscent of the Mothers, could appear as a beautiful woman or as a crow, as could the Morrígan. The Dísir appeared in similar guises. In addition to being battle goddesses, they are significantly associated with fate as well as birth in many cases, along with appearing before a death or to escort the deceased. It is interesting to note that some sources present Éire and the Morrígan as half-sisters.
The concept of a raven goddess of battle wasn't limited to the Irish Celts. An inscription found in France invoking Cathubodva, 'Battle Raven', shows that a similar concept was known among the Gaulish Celts.
The Morrígan's role is quite similar to the role played by the Valkyries in Norse cosmology. Both use magic to cast fetters on warriors and choose who will die.
During the Second Battle, the Morrígan said she would go and destroy Indech, son of Dé Domnann, and deprive him of the blood of his heart and the kidneys of his valor, and she gave two handfuls of that blood to the hosts. When Indech later appeared in the battle, he was already doomed.