Unsure of Cowl's birth name or public identity. I tend to think unmet character. However, as for what his intentions are, I'm piecing together ideas. Here we go:
To my knowledge, we have three confirmed on-screen appearances of Cowl in the series: (1) Bianca's Ball in Grave Peril, (2) the events of Dead Beat, and (3) as a handler/master of Vittorio Malvora in White Night.
(1) In Grave Peril, Cowl and Kumori (we reasonably assume) are responsible for giving Bianca the box containing Morgana's Athame, which she in turn gave to Harry's godmother, Lea. I don't recall at present if they also gave Bianca what she offered to Ferrovax or not. We know as of Cold Days that the Athame caused Lea to become Nemfected. That may or may not have been Cowl's intent. Apart from the Nemfection, it was also an item of prodigious magical power given to a high-ranking member of the Winter Court. Mab had to rebalance the scales of power after Lea returned with it.
Intention (reasonable speculation): either to influence Winter politics by strengthening the power of one of its members, or to gain a Nemfected operative in Winter, or both.
(2) In Dead Beat, Cowl and Kumori are one of the three teams of Kemmlerites attempting the Darkhallow, and arguably the real planners of it in the first place. Despite their claims to only wish it to prevent Grevane and Corpsetaker from misusing the power, evidence suggests that Cowl would have wanted to go through with it even if the other Kemmlerites were absent. Bob says that Cowl was probably the only one who knew the ritual must be done on Halloween, suggesting he was involved in planning the timing of the Red Court attack. Kumori tells Dresden that Cowl wants to end death, and obtaining the power of the Darkhallow would be a big step forward in that direction. And nothing about Cowl's expressed personality says he despises the idea of additional power.
Intention (reasonable speculation): acquire power on par with a Faerie Queen, and use said power to depose the current Senior Council, overturning enforcement of the Laws of Magic in allowance of pursuing either unmolested necromancy, increased Outsider summoning, or both.
(3) In White Night, following an assumed recovery period after failing to perform the Darkhallow, Cowl (assumed) is witnessed in authority over Vittorio Malvora, involved in a White Court power play. This play targeted Raith specifically. Given that it is almost common knowledge that Lord Raith is only boss de jure, and Lara boss de facto, I suspect this attack to have been aimed largely at her vision for House Raith (at the time, she was proposing peace with the White Council, IIRC). When that power play fails, Vittorio calls in Cowl with an army of uber Ghouls to destroy the leadership of the White Court. From what I recall, only some high members of House Raith escape. Houses Malvora and Skavis are basically removed as players from White Court politics in the aftermath.
Intention (reasonable speculation): depose House Raith as head of the White Court, and failing that, devastate the leadership of the entire court. In doing so, the White Council would remain under pressure, and Lara Raith (whom we have since learned is associated with the Venatori) would be out of the picture.
Inferences and Conjecture: Kumori's assessment of Cowl's objectives to end death is loosely true. Maybe it's misguided altruism (ha), or maybe it's self serving (more in character).
In his struggle to achieve this, in addition to dabbling in necromancy, Cowl deliberately summoned Outsiders for power. He became Nemfected, but believes himself to be manipulating the Outsiders in whatever bargain they offered him for additional power. The actions he has taken have all had intentions that align with the goal of the Old Ones/Outsiders to bring down the Outer Gates and cause Empty Night: spreading Nemesis into Faerie, attacking the power of the White Council, and hurting agents of the Venatori (players in the Oblivion War to keep the Old Ones outside Creation).
Though Nemesis has its own purpose for Cowl, if Cowl really wants to end death, his actions so far do align with that goal. Ending death would involve acquiring a great deal of power (Darkhallow), destroying or damaging powers that would resist his efforts (White Council and their Laws of Magic), and destabilizing Faerie (Athame). Why Faerie? Because the closest known being we have to wielding the power of death itself is none other than Atropos herself, Mother Winter.
Why end death? Kumori gave a list of reasons. Cowl could agree with them, though I suspect that's a line he uses to string her along, and possibly justify it to himself. He could also just not want to die. Or, there could be someone/multiple someones that he doesn't want to die, or even wants to resurrect. Not altruistic, but not self serving either. This may have been his original desire, which was then corrupted by exposure to Nemesis. We are told that it turned a man''s love for his family into a lust for power (Victor Sells), it corrupted officers of the law into becoming worse than the kind of thing they tried to destroy (Agent Denton), and it influenced the whole Nightmare debacle (Leonid Kravos).
Proposed sequence:
Enter Cowl, talented and noble wizard
Either death of loved one, or impending death of one for Cowl
Search for remedy in Necromancy, corrupted by Black Magic
Search for remedy in Outsiders, corrupted by Nemesis
Join the Circle, group of Nemfected wizards collaborating with Outsiders for what they think are their own reasons
Become Darth Ringwraith, Wielder of Black Magic to Destroy Death Herself and, in the process, inadvertently hand Creation to the Outsiders
TLDR: The Outsiders are using Cowl by dangling the idea of destroying death in front of him. The steps to do this, with which they would graciously cooperate, involve deposing the White Council and gaining access to the power of Mother Winter. By a happy coincidence, these steps also work toward destroying the safeguards that prevent the Old Ones and Outsiders from rising again and bringing about Empty Night.
That's all I've got so far. I don't buy into any of the currently known characters are Cowl theories because each one has enough against it that it doesn't make sense.
No Justin - Word of Jim is he's dead
No Kemmler - see above
No Time Traveling Harry - not enough reason to suspect this
No Alterna Harry - also not enough reason to suspect this, and we're told Butcher already has different plans for an Alterna Harry
No Simon Pietrovich - Ebenezer said Simon was a friend. Don't think he would have befriended someone that into necromancy
None of the current Senior Council seem to make sense. The closest would be Cristos, but his mannerisms that we've heard don't seem to mesh with what Cowl's shown so far.
No Alterna Justin - this one I could almost see working, but I don't know why we should suspect this at the present.
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