The Morrígan ("the Phantom Queen" or "the Great Queen") was the Irish goddess of battle, of sovereignty (in a particular sense — sovereignty as represented by the goddess who married or selected each rightful king), and of prophetic vision. She often appeared in triple form, herself and two others (Badb and Macha; or, in some traditions, the three sisters Morrígan, Macha, and Nemain) — a triple-goddess pattern of considerable Indo-European antiquity. Her favored shapes were those of the crow, the eel, the wolf, and the heifer; she changed shape often in narrative, particularly when she encountered the great hero Cú Chulainn (treated below), with whom she had a complicated relationship: she desired him, was rejected, fought him, healed him, prophesied for him, and finally — at his death — perched in crow-form on his shoulder as the sign that he was indeed dead.

Her tryst with the Dagda before the Second Battle of Mag Tuired, told under the Dagda's entry above, illustrates her sovereignty-aspect: it is by her bestowal of favor (sexual, prophetic, military) that the Tuatha Dé win the battle. The figure of the goddess of sovereignty whose ritual marriage with the king secured his rule has been recovered by modern scholarship from many strands of Irish tradition (Gerald of Wales reports an Ulster king's literal mating with a white mare in his coronation, a procedure that the Irish themselves may have considered already long obsolete by Gerald's time, but that preserved the older pattern). The Morrígan's continental Gaulish parallels are uncertain; the Romano-British Cathubodua ("battle crow") attested in inscriptions corresponds to one element of her complex.