The Morrigan is an ancient Irish goddess;
the  goddess of battle, strife, and fertility. 

She is both a single goddess and a trio of goddesses:
Badb, Nemain and Macha.

The Morrigan is the goddess of victory.

On battlefields, she often appears as a raven or crow.
She is the dispenser of courage and fear
and many a battle has been decided through those emotions rather than battle prowess.

Origin The origins of the Morrigan seem to reach directly back to the megalithic cult of the Mothers. The Mothers (Matrones, Idises, Disir, etc.) usually appeared as triple goddesses and their cult was expressed through both battle ecstasy and regenerative ecstasy. It's also interesting to note that later Celtic goddesses of sovereignty, such as the trio of Eriu, Banba, and Fotla, also appear as a trio of female deities who 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." (Ross 205)

Eriu, 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 Morrigan. The Disir 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.

There is certainly evidence that the concept of a raven goddess of battle was not limited to the Irish Celts. An inscription found in France which reads Cathubodva, 'Battle Raven', shows that a similar concept was at work among the Gaulish Celts.

Valkyries in Norse cosmology. Both use magic to cast fetters on warriors and choose who will die.

During the Second Battle, the Morrigan "said she would go and destroy Indech son of De 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." (Rees 36)

Compare this to the Washer at the Ford, another guise of the Morrigan. The Washer is usually to be found washing the clothes of men about to die in battle. In effect, she is choosing who will die.

An early German spell found in Merseburg mentions the Indisi, who decided the fortunes of war and the fates of warriors. The Scandinavian "Song of the Spear", quoted in "Njals Saga", gives a detailed description of Valkyries as women weaving on a grisly loom, with severed heads for weights, arrows for shuttles, and entrails for the warp. As they worked, they exulted at the loss of life that would take place. "All is sinister now to see, a cloud of blood moves over the sky, the air is red with the blood of men, and the battle women chant their song." (Davidson 94)

An Old English poem, "Exodus", refers to ravens as choosers of the slain. In all these sources, ravens, choosing of the slain, casting fetters, and female beings are linked.

"As the Norse and English sources show them to us, the walkurjas are figures of awe an even terror, who delight in the deaths of men. As battlefield scavengers, they are very close to the ravens, who are described as waelceasega, "picking over the dead"..." (Our Troth)

"The function of the goddess [the Morrigan] here, it may be noted, is not to attack the hero [Cu Chulainn] with weapons but to render him helpless at a crucial point in the battle, like the valkyries who cast 'fetters' upon warriors ... thus both in Irish and Scandinavian literature we have a conception of female beings associated with battle, both fierce and erotic."

Morrigan visualization exercise:

You are within the green glow of the living earth,
Feeling the sphere of the globe
As the physical extent of your body,
The manifestation of your flesh.
The seas are the flow of your blood,
The mountains are your bones,
The winds your breath.
The roads and cities are your nervous system,
The dreams of humanity your mind.
And throughout this body
There is warfare and destruction,
An there is the making way
For the New life
There is anger and contention
And there is friendly competition
The cry of teams and players
There is negative conflict
There is positive competition
In the midst of both
There is crackling energy
There is the strength
The power
The Great Warrior Goddess
Who wears two faces
It is the Goddess who is the world,
It is she who fights in every battle
Who competes in every race
And in her rage and frenzy
Joy and ecstasy
You sense the defense of the good
And the opposing of evil.
In the ceaseless struggle of the people
Are the birth-pangs
Of a better future striving to be born.
In the revolutions are cries for justice,
In the wars are a reaching for peace,
In the violence a need for self-defense.
In all of this rough play
The mind of the world is striving
For better dreams,
And the heroes strive to defend what they love.
And this is Joy of Morrigan!
For we are all one world,
One life, one flesh;
And life is struggle, competition and joy
And from lesson you turn away,
Falling back to where you began,
To breathe in the healing and hope of the world
The energies of strength
And compassion.

From the author "Ultimate Guide to Goddess Empowerment" by Sophia