モリガンの最も古い資料は、ラテン語写本の中の用語集とグロッサリー(用語集)である。9世紀のヴルガータ版『イザヤ書』の写本には、ヘブライ語の「リリス」を訳すために「ラミア」という言葉が使われている<ref>Isaiah 34:14 "And wild beasts shall meet with hyenas, the satyr shall cry to his fellow; yea, there shall the ''night hag'' alight, and find for herself a resting place." (Revised Standard Version, emphasis added)</ref>。これを「女性の姿をした怪物、つまりモリガン」と説明する解説書がある<ref>Epstein, 1998, pp45–51</ref>。コーマックの『用語集』(同じく9世紀)と後期写本H.3.18の注釈では、複数形のgudemain(「妖怪」)をモリガーナ(morrígna)という複数形で解説している<ref>DIL, 1990, p372</ref><ref>Epstein, 1998, pp45–51</ref>。8世紀のO'Mulconry's Glossaryには、マッハは3つのモリグナ(morrígna)のうちの1つであると書かれている<ref>Epstein, 1998, pp45–51</ref>。
===Ulster Cycleアルスターサイクル ===
The Morrígan's earliest narrative appearances, in which she is depicted as an individual,<ref name="CELT-Regamna">{{cite book |url=http://www.ucc.ie/celt/online/G301005/text002.html |title=Táin Bó Regamna |work=Corpus of Electronic Texts Edition |page=33 |author=Unknown}}</ref> are in stories of the [[Ulster Cycle]], where she has an ambiguous relationship with the hero [[Cú Chulainn|Cúchulainn]]. In the ''[[Táin Bó#Tains|Táin Bó Regamna]]'' ("''The Cattle Raid of Regamain''"), Cúchulainn encounters the Morrígan, but does not recognise her, as she drives a [[cow|heifer]] from his territory. In response to this perceived challenge, and his ignorance of her role as a sovereignty figure, he insults her. But before he can attack her she becomes a black bird on a nearby branch. Cúchulainn now knows who she is, and tells her that had he known before, they would not have parted in enmity. She notes that whatever he had done would have brought him ill luck. To his response that she cannot harm him, she delivers a series of warnings, foretelling a coming battle in which he will be killed. She tells him, "It is at the guarding of thy death that I am; and I shall be."<ref>"[http://www.maryjones.us/ctexts/regamna.html The Cattle Raid of Regamna]", translated by A. H. Leahy, from ''Heroic Romances of Ireland'' Vol II, 1906</ref>