Is there any connection between Odin and the Irish Goddess Morrigan?

Question

At first glance, these two gods seem to share just a single aspect - an association with war. But digging a little deeper there seems to be a similarity between the function of Odin's maiden, the valkyries, and the Great Queen. The Prose Eda describes the valkyries like this:"these women are called valkyries, and they are sent by Odin to every battle, where they choose which men are to die and they determine who has victory". So it seems they controlled the tide of war. But that also appears to be an aspect of the Morrigan. In the Táin Bó Regamna , she foretells the death of Cu Chulainn and in other myths she is credited as granting courage to warriors or frightening enemies, turning the tide of battle. In terms of connections with Odin himself, they both have an association with warrior bands and bandits living in the wild. Morrigan has the fianna, who seem to have revered her, and Othin is associated with bands of berserkers and outlaws. So is there any form of connection?

Answer 1

Indeed, as you pointed out, the similarities between the Morrígains (or equivalently, the Bodbs) and the Valkyries are quite striking, as summarized by Matthias Egeler in Celtic Influences in Germanic Religion: A Survey:

The characters of the Valkyries and the Bodbs appear to exhibit extensive parallels: both classes of supernatural beings are (1) female beings who can appear (2) both as a group and as single individuals, who are (3) fundamentally located in the realm of death, (4) deeply concerned with war, (5) can display a noticeably erotic trait in their dealings with the male protagonists of war, (6) are associated with birds and a bird-shape and (7) have a direct lethal influence on the mind of their victims.

He then goes on to argue in favor of a direct connection between the two, due to Celtic-Germanic interactions in continental Europe, way earlier than the Viking age:

[...] indeed the first attestations of the Valkyries in Norse literature are too early to allow the possibility that the Valkyries could have been borrowed from Ireland during the Viking Age (nor is it possible to assume a borrowing in the opposite direction).

Interestingly, he also draws a parallel between the "the female battlefield demons of Ireland and Scandinavia" and other figures from Classical Mediterranean mythology, such as the Greek Sirens, Erinyes, Harpies and Keres, the Roman Furies, and the Etruscan death-demon Vanth.

Regarding the connection with warrior bands and their "divine frenzy", the following passage from War Goddess: The Morrígan And Her Germano-Celtic Counterparts by Angelique Gulermovich Epstein (which I highly recommend you read in its entirety, if you are interested in the subject) is certainly relevant:

Perhaps the Morrígan herself (or at least her divine fury), personified as a bird, possesses the warrior, as Odin (or his fury) enters the berserk.

However, it should be emphasized that, while there is plenty of archeological and literary evidence supporting the historical existence of a cult of Odin in the Germanic world, no cult of the Morrígan seems to be attested in the Celtic world.