Origin
In life, she was known as Nimue, and lived during the reign of King Arthur, and was beloved by Merlin, who told her all of his secrets. She used this knowledge to imprison him alive inside of a grave, but, without Merlin to guide her, it drove her to madness and eventually to worship the Ogdru Jahad. Her powers were so great, that all the other witches killed her, cut her into many pieces and scattered them all over the earth. However, the pieces would always rejoin, so they imprisoned inside of a box and buried her deep within the earth.
Darkness Calls
While the witches of Britain try to find a new leader, Gruagach arrives at their meeting and nominates her; despite their reservations, they agree. Arriving in a church somewhere in England, Gruagach and his two companions kill the monks inside and descend into a cavern below the church, inside of which is a large, sealed hole. He gives the giant guarding the cave a letter from the witches of Britain, giving him permission to remove the unnamed prisoner from her captivity in the hole. The giant returns with a wooden box and, after giving it to the trio, descends into the hole, telling Gruagach that he does not wish to see what will surely ensue if she's released.
The Wild Hunt
Upon a hilltop, surrounded by a large army, Gruagach is approached by an old man who turns out to be Astaroth in human form. He gives Gruagach a Ciborium that contains the blood of the inhabitants of a nearby human village. After pouring the blood into the box, the Queen of Blood arises.
After settling her score with the remaining Witches of England, she demands that an army be marshaled for her. She continues to sit upon the hill, telling Gruagach that her army is coming. She also tells him that her followers are currently searching for Hellboy, and promises that when the time is right she will make Gruagach strong again and that she will deliver Hellboy to him.
She is then greeted by an ambassador from Uddsvik, the king of Jutland. The messenger relays warm regards from the king, who brings promises that he and all the kings of the north will have their armies fight for her. After the messenger presents her with a crown, she tells him to hammer into a knife so that he may murder his king, cut out his heart and throw it into a furnace so that the fire burns red. She then tells him that in the same furnace, he should make her an iron helmet in the shape of three ravens joined together and carve into it three names: Badhbh, Macha, and Mor-Rioghain, so that all will know her not as the Queen of Witches, but as the Goddess of War.
Later, when Hellboy retrieves the sword Excalibur, she wonders what Morgan Le Fay has planned and says that it makes no difference. As she continues to wait for the arrival of her army, Gruagach demands that she make him strong again. When he suggests that she lacks the power to do so, she flies into a rage and casts him away before disappearing with her followers.