Cowl is Justin and Elaine is Kumori. Time to drag out this old theory again.

Cowl:
1. Cowl has appeared in several books - first notable one is Death Masks at the Bianca's ball. He delivers a gift (possibly nemfected) to several guests, but only confirmed through Mab about the Leansidhe. Morgana's Athame is traded for Amoracchius (Excalibur).
2. In Dead Beat Cowl mentions many things of significance happened that night, Dresden is only aware of a few of them. Cowl likely conspired with Mavra and Bianca and her progenitor (Ortega), who's wife Ariana was part of the group that Margaret Le Fey, the White King, and possibly Justin Dumorne were all a part of. A group that might have decided it was time for the White Council to end.
3. A shadowy figure sponsors and is seen in White Knight. Harry seems to recognise his magic as Cowl's. In this book, the Circle is mentioned for the first time.
4. Cowl is an expert at Evocation, Neuromancy, Veils, Ways and Necromancy. He also mentions his skill at swordplay. Why would Cowl have a sword? Most wizards do not carry them. But an ex-Warden would. All his magical skills and talents would make him an excellent warden (excluding the fact he can't use Necromancy).
5. Justin is likely a skilled Nueromancer - he enthralls Elaine before Harry gets to the confrontation.
6. Justin was in the assault on Kemmler. Cowl says he despised the "mad man" Kemmler, despite being his student. He may well have taken the opportunity to erase his enemy for his own ends.
7. Justin was Simon's apprentice. It is stated in Summer Knight that Simon's fortress was impregnable, and the Warden's forensics suggest that someone let them in past the defences. Eb says it would still have required someone who knew the place inside out. Justin is only discounted on being dead, but otherwise as a rogue Warden and Warlock would have been a candidate, who the Council suspect passed on the knowledge to Harry. Now we know that it wasn't Harry - so it doesn't leave much leeway.
9. Simon is said to have been found dead, along with the brute squad. Whilst it doesn't explicitly state his body was found, it would be a hell of a thing for them not to notice his missing corpse. A whole plot point in the series is built around how intolerable it would be to have a high-level wizard turned to the enemy. A missing Senior Council member might have provoked a stronger reaction.
10. We only have Harry's word that Justin died, and that he fought Justin in earnest. Most people thought is unlikely he beat Justin. Fires in stories tend to be useful covers for other events, a physical symbol of chaos.
11. Jim says Justin is dead. D-E-D dead. He has also said not to trust a word he says. JB has also described death as "a squishy line in the Dresdenverse"
12. Many characters, including Mab, have said Death is a spectrum.
13. Harry believed Elaine was dead. Harry was wrong. If he was wrong about her...
14. From a writing perspective, consider Star Wars (one of Jim's favourite stories). Luke is raised an orphan by others, his lovely aunt and uncle. He then goes on an apprenticeship with a wise old mentor. He is told his father was a Jedi, who his most feared enemy killed. Vader reveals he is Lukes father, which Luke is in denial about but realises must be true. Obi-wan does the fae-speak of half truths (When your father became Vader, he killed Anakin Skywalker). The trope of Harry thinking his foster father and first mentor is dead, who actually isn't would be a good technique and mess with Dresden's psychology majorly.
15. Cowl hides his face, the other Necromancer's do not. Harry suspects White Council. He might be right, but likely that is not the only reason. They even distort their voices. Vader hides his face too - and was a jedi once. Luke just did not know it.
16. Cowl wishes to end Death. Why? The Outsiders might want that, perhaps it would limit the power of TWG. But why would Cowl? Kumori seems to believe him. I suspect it is because he is traumatized by the Death of someone he loved.
17. Justin and Cowl both have links to HWWBH.
18. If Justin is dead, why no Death Curse?

Kumori:
1. Kumori is tall enough to hold a knife to Harry's neck - Harry is 6'9" roughly so not an easy feat.
2. Elaine is described as being tall, tall enough she only has to stretch a little to kiss him on the cheek.
3. Elaine is described as being a better at magic than Harry, while Harry is brawnier. She is skillful enough she is not worried about people seeing through her veils. 
4. Kumori seems to use less brawn and more subtler magic than Cowl; less of a duelist but still deadly.
5. Kumori is a distinctly japanese name.
6. Elaine uses japanese as her magic words.
7. Kumori shows compassion - she resurrects a dead gunman of Marcone's for apparently no other reason than because she thinks she should.
8. Elaine has shown much compassion for her fellows, whilst still distrusting the institution of the White Council.
9. Elaine was the Emmisary of Summer/Harry's opposite. She says she was part of the Summer Court for a long time. Summer has been involved unusually in the books. Mostly ambivalent or directly in contest with Dresden. Rarely against the foes of Dresden.
10. Kumori and Elaine show compassion for Dresden, but not so much that it impedes their goals.

Bit of a wild theory here. I believe Justin was in love with Maggie. They had a relationship and they both felt the White Council was too harsh and too rigid. Maggie and Justin had two children - Elaine and Harry (perhaps twins?). Elaine is older than Harry - he is always referred to as Margaret's youngest. When Maggie was killed by the White Court - Justin was furious. But he could not yet move against them. He finally gets his children back when Malcolm died. He raises them to be his disciples and enforces but it goes wrong and he either dies and is revived or fakes his own death. He finally gets his revenge by "accidentally" murdering half the White Court when his uber-ghouls start murdering everyone. He definitely would want to end Death as he is still grieving Maggie.

From a writing perspective (and fitting nicely with the Star Wars inspiration) - it would be a major shock to discover not only is Justin alive, but he is Cowl and been orchestrating all the terrible stuff in Dresden's life. It would also majorly freak Dresden out is he realised Elaine was his sister, something Justin would have definitely encouraged (like a good cult leader). It also matches the weird Luke-Leia thing. Finally, you might argue Dresden should have recognised Justin's magic. I think he sort of did without realising it. Cowl's magic is human, with a bit of Dark Magic in it - unlike the Mavra or even the Corpsetaker. Harry recognises so is his, which makes sense when you realise he was taught all the basics by Justin/Cowl. I also believe Justin will likely kill Ebenezar while he tries to protect Harry. Very common trope. Harry might find it very hard to be good when he realises his whole life is a lie, he was born to be a weapon, he commited incest (potentially) and that his mother was in on it for a long time. Harry is given power over Outsiders. Yes he uses this as a weapon - but perhaps the real purpose is to be a leader (very Hellboy in my mind).

Anyway, have at it. Let's debate this all again!

Very true - they all fit the bill to a degree. However the issues I found when examining them as candidates is that Molly and Murphy are love interests (not great if you are a twin...) and Thomas is his brother but not actual twin (which would make more sense if he was the archetype, and he is male and the twin dichotomy for the theory is male/female). I certainly understand where you are coming from, but the way I see it coming about is thus:

Harry and Elaine are both starborn (twins not necessarily in blood, but in conjunctions, perhaps even on polar opposite conjunctions). They are raised and trained by Dumorne, then the falling out happens and Harry leaves after appearing to kill Justin and Elaine. However, Elaine returns and my guess is Justin survived too - how else did Elaine survive? She was enthralled at the time and Justin was the most powerful Wizard in the room at that time. I suspect he is Cowl and Elaine is Kumori, and that in the end she will betray Justin and stand with Harry against the Old Ones in the BAT.

Good boy!

Margaret le Fay died due to the powerful malacchio curse, like the Barabass curse, that causes horrible deadly misfortune on the recipient. This spell was done by the White King Lord Raith, possibly with the help of a cult of practitioners and potentially even He Who Walks Behind.

However, malacchio can mean "evil eye". Who has an evil eye in mythology? Well one interesting individual does: King Balor of the Fomor. Known for his singular eye that killed all it looked upon, he was a ruthless tyrant and terrifying opponent. But what if it was not his eye, or even his physical eye, but the eye was a power he was given through his daemonic (Outsider) heritage from HWWB? This could make a lot of things very personal for Dresden.

Yeah but Jim said that anyone on the Council would mop the floor with Harry.  Langtry also appears to be very good at mind magic...  I think he'd have assaulted Harry's mind to test him rather using kinetic force.

I specifically believe he was referring to Senior Council at that time. Of the thousand plus wizard in sheer might, even before he became the Winter Knight, Harry always saw himself in the top 30-40 strongest. Which is not to say most capable fighters or most powerful wizards. Even though I suspect he has had a pretty meteoric rise in combat ability over the series. Jim has even gone back and said not every wizard, not even most wizards are suited to combat. That was why there was only 200 wardens in a thousand plus group. And of the senior council only Simon (dead), Eb (who replaced him, and is also the Blackstaff and was captain of the wardens), Langtry (the Merlin), Rashid (the Gatekeeper), Listens-to-Wind and Cristos are fighters and skilled in Evocation. Martha Liberty, Aleron Lafortier (dead), Ancient Mai are all considered to have talents that do not lend themselves to direct combat. Though I acknowledge Liberty is an unknown quantity here, all we really know is she is good at veils.

An odd choice considering the Queens scale up - lady<queen<mothers. So knight<fae king<sage (?) The gatekeeper is unlikely as powerful as the mothers - considering they outrank just about everything apart from archangels.

The etymology of the name is debated. The first part is now generally agreed to be the Old Irish fo, meaning under, below, lower, beneath, nether, etc. The meaning of the second part is unclear. One suggestion is that it comes from the Old Irish mur (sea), and that the name thus means something like "the undersea ones".[5] This was the interpretation offered by some medieval Irish writers.[6] Another suggestion is that it comes from mór (great/big) and means something like "the great under(world) ones", "the under(world) giants" or "the nether giants". A third suggestion, which has more support among scholars, is that it comes from a hypothetical Old Irish term for a demon or phantom, found in the name of The Morrígan and cognate with the archaic English word "mare" (which survives in "nightmare").[7][8] The name would thus mean something like "under(world) demons" or "nether demons". Building on this, Marie-Louise Sjoestedt interprets the name as meaning "inferior" or "latent demons", saying the Fomorians are "like the powers of chaos, ever latent and hostile to cosmic order".[4]

Interpret that how you will. They also have some interesting links to Noah, and to Perseus in Greek Mythology. Jim does his homework.

ALSO:The Fomor are supernatural demon-kin who dwell in the cold, dark waters. Folk tales say they are ancient evil gods – the personification of death and blight, but many have proven that they are not as all-powerful as told. The Fomor were described as having a missing body feature, such as an eye, leg, arm or all 3! Some have heads akin to reptilian goats and many have tails or other features to help them swim. Being creatures of magic and borne of daemons could be Outsider blood in them  - Ed note, no two fomor look identical and are instead categories by size and power.

Hi gang,

In further research and meanderings I was reading a little bit about the relationship between the Horned God and the Triple Goddess in Wicca/Celtic mythology.

The pentagram is interesting. In Wicca, the two horns represent balance and are two points of the star, and the other points represent the Triple Goddess. This fits nicely with the nature of magic (the combination of the natural elements and magic) and the druid origins of the white council (the OG Merlin being originally a druid as well as a wizard).

Now Jim has mostly slotted the Horned God into the role of the Erlking/Herne/Cern, however I took interest in the part about the Warrior (youth), the Father and the Sage.

Now Herne and Kringle could be considered Fathers. Warriors/Youths correlate nicely with the Knight (though I am not sure this was intentional by Jim) but where is the Sage? This would be something akin to the Mothers, something unmentioned so far with no hints. I can only think of TWG or Archangels, but it seems a bit of a stretch.

Any thoughts?