Cowl

Cowl is a human wizard and necromancer. He first appears in Grave Peril and is named in Dead Beat.

Description
Cowl is an unknown, extremely powerful wizard, who is power-hungry, but seemingly sane. He may actually be one of the wizards on the White Council, or someone entirely different. His face has never been seen, and his real name is unknown. He could have been part of the White Council. Cowl informs Harry that "The Council is not what it once was. It's rotted from the inside, and many wizards who have chafed at its restrictions have seen the War with the Red Court reveal its weakness. It will fall. Soon."

In Dead Beat, he attempted to gain the power of a minor god with the Darkhallow ritual. Bob believes that Cowl knew that Halloween is the only time to perform the Darkhallow. Bob said of Cowl, "That guy is seriously scary."

Cowl and Kumori were dressed nearly identically in long black robes, long black cape, big black mantles, big black hoods which revealed nothing of their faces.

Cowl stated that "a great many things of significance happened that night" at Bianca's Ball, the majority of which Harry is not aware of yet.

When Harry calls Cowl a Kemmlerite, his answer was of disdain for the madman Kemmler.

He's been associated with his subordinate Kumori, Vittorio Malvora (who was working with Madrigal Raith) and part of the Circle, which might indicate his membership to the Black Council.

Powers
Harry judged that his power was Senior Council level; Cowl hit him harder than Ebenezar or the Leanansidhe.

Cowl's magic is described as not necessarily black, and human, but tainted like Harry's. He's a powerful necromancer, though he denies being one of Kemmler's disciples.

His skills at opening up portals to the Nevernever are better than Harry's and he is also able to close other practitioner's portals from a distance. He can sense other practitioners from a distance.

Cowl can appear to be something he's not—he came up behind Harry as a zombie lifting his spear, then shimmered into his robed self and threw out a spell at Carlos Ramirez that threw him twenty feet. Then he quickly blocks a Hellfire-strengthened kinetic blast that Harry aims at him by crossing his arms in an x-shape, which only put him off balance.

Grave Peril
In Grave Peril, two unnamed hooded figures, fitting the description of Cowl and Kumori, appeared at Bianca's Ball. One of them held out to Ferrovax a small cask about the size of a breadbox, opened it—"the lights gleamed on something that sparked and shone." They also handed the box containing Morgana's athame to Bianca to give to the Leanansidhe.

Dead Beat
In Dead Beat, Harry meets Cowl for the second time, where he's searching for Die Lied der Erlking and The Word of Kemmler with Kumori, his assistant. Harry recognized them from Bianca's Ball as the ones who gave Leanansidhe the athame. Harry flips a car onto him and manages to escape with the aid of Billy Borden and the Alphas. Cowl knew that Harry possessed Bob the skull, and took it in order to learn how to perform the Darkhallow. With Bob, he had no need for the Word of Kemmler. Cowl disappeared after the workings of the Darkhollow were disrupted.

At the end, Harry tells Morgan and Listens-to-Wind that he thinks Cowl had a deal with the Reds to keep the Council busy while he performed the Darkhallow. The Reds would get the Senior Council out of the deal. Morgan thought the Edinburgh defenses were nearly impenetrable - it would take a god to break through Edinburgh's defenses. Cowl would have obtained that much power after performing the Darkhallow.

White Night
In White Night, With the aid of Little Chicago, Harry followed Grey Cloak to a meeting with Cowl in a miniature hologram-like form (similar to Star Wars). He sensed that Harry was there eavesdropping and zapped him. Harry barely escaped getting fried.

Later, when Vittorio Malvora was about to lose the duel, he summoned Cowl, calling out "Master!". Cowl entered though a Way, bringing ghouls to the White Court conclave in the Deeps, which may imply that he was also a part of the New Mexico incident involving the murder of the Trailman Twins at Camp Kaboom—Harry felt the same echoes of power that he felt in the cave in New Mexico.

Quotes
Cowl: "I was the only one of the three of us who thought you would succeed [in summoning the Erlking]." Harry: "I thought you guys hate one another's guts. Are you working together or trying to kill each other?" Cowl: "Why yes. We smile at one another and play nicely all in the name of Kemmler's greater glory of course. But we are all planning on killing one another as soon as it's convenient."