A common question that I hear people asking is what does the Morrigan look like. There really isn't a simple answer. Generally when she appears in mythology she is not described in much detail. Instead we get passages like this one from the Cath Maig Tuired:
(The Unish of Connacht calls by the south. The woman was at the Unish of Corand washing her genitals, one of her two feet by Allod Echae, that is Echumech, by water at the south, her other by Loscondoib, by water at the north. Nine plaits of hair undone upon her head.)
Similarly when she appears in most versions of the Tain Bo Cuiligne* (TBC) it simply says "Is ann sin tainic in Morrigan ingen Ernmuis a Siodaibh" (Then came the Morrigan daughter of Ernmas from out of the Sí) without adding any physical details. There are a few appearances which are described however.
In the Táin Bó Regamna (TBR) we are given this: "Bean derg hissin charpat ocus bratt derg impi ocus di braí dergai lé ocus a brat eter di feirt in charpuit síar co sliged lár ina diaig..." (A red-haired woman with red eyebrows was in the chariot with a red cloak around her shoulders; the cloak hung down at the back of the chariot and dragged on the ground behind her.) This description of a red-haired woman** may be the most detailed description we ever get of the Morrigan's physical appearance and it is the only one where we are never told that she is in disguise or in an assumed form. In my own opinion this is most likely to be her true appearance, but other people may have different conclusions.
This description is somewhat similar to another of the Morrigan's appearances in the TBC: "And-sin tánic in Mórrígu ingen Ernmais a Sídib irricht sentainne" (then came the Morrigan daughter of Ernmas from out of the Sí shaped as an old woman). However this passage makes it clear this is not her natural appearance but a "richt", a guise, form, or assumed shape. The idea of the Morrigan taking on other shapes or disguises is a common one, and in fact in the Metrical Dindshenchas she is called "samla día sóach" (a phantom, the shape-shifting Goddess) making it clear that her form is fluid and changeable.
It is debatable whether or not the brief description of the Morrigan in disguise as "Buan's daughter" in the TBC reflects her true appearance or is, as with her form as an old woman, merely a disguise. In this passage, which does not occur in all versions of the TBC she is described as "in n-ócben chuci co n-étuch cach datha impe ocus delb roderscaigthe furri" (the young woman with a garment of every coloring around her and a form fiercely beautiful on her). Personally I'm a bit suspicious because of the phrase "delb...furri" that is "a shape...on her". It is possible that it's just an expression, or perhaps it could be an allusion to the fact that the Morrigan has assumed this alluring disguise as part of her attempt to trick Cu, who has of course seen her red-haired form in the TBR previously.
She also has several animal forms which are described in the TBC as "escuinge slemne duibi" (a smooth, black eel), "saidhi gairbi glasruaidhi" (a rough, grey-red bitch), "samhaisci finne óderge" (a white, red-eared heifer) and in the TBR we see these forms echoed in her threats to Cu Chuluinn: "esccung" (an eel), "sod-sa dono glass" (a blue-grey*** wolf-bitch), and "samuiscc-siu finn áuoderg" (a white, red-eared heifer) as well as "hén-si dub" (she, a black bird). In the Lebor na Huidre she is also described as taking the form of a bird "in Mórrigan són i ndeilb eúin" (the Morrigan, she in the likeness of a bird). It is interesting to note that most of these animal depictions come with a specific color.
The Morrigan is clearly capable of assuming many forms to serve her purposes, and we have descriptions of many of them. I have only touched on some here to illustrate what we generally know about her appearance. It may be that her true form is of a a red-haired woman dressed in red, as we see in the TBR, but certainly she is not limited to that. She comes to us in many shapes and forms, through many guises and many means. Ultimately she is what she chooses to seem to be to each viewer, whether that is black bird or white cow, naked hag or fiercely beautiful young woman.
** literally the text says "bean derg" a red woman, however in Irish this is how hair color is usual given. See Audrey Nickel's "Color Me Irish" blog post for more on this
*** for those who are interested in the use of color in Irish material its given here as glas, or literally green, but green which can be anything from a light green or blue to a blue grey.
The Morrigan has many guises and I have met most of them in the flesh, from Strong sweet and loving to brave and assertive to the don't mess with me ever types.
Nicely done! Well researched and written. She had much about her open to interpretation, especially her appearance.