Anduriel

Anduriel is a Fallen Angel and hosted by Order of the Blackened Denarius member, Nicodemus Archleone. He first appears in Death Masks.

Description
"Nicodemus’s lips moved, but an entirely different voice issued from them—something musical, lyrical, and androgynous."

- Anduriel’s voice described

Anduriel has been in the possession of the human known as Nicodemus Archleone for an extended period of time which exceeds 1500 years, given that his daughter was at least this old prior to her death at his hands. While many of the fallen prefer to dominate their hosts will, Nicodemus and Anduriel prefer to work in concert, with Nicodemus remarking that he does "not dance to the fallen's tune", but rather that he "set[s] the beat" despite moving together. This relationship appears to be an equal partnership which gives Anduriel more power because he can utilize his host's free will to a greater extent.

He appears to manifest as Nicodemus' animated and corporeal shadow, which can suppress the magic power of human practitioners in a similar manner to thorn manacles, as well as directly assist Nicodemus in combat.

While fully capable of the raw strength and combat abilities of any of the Fallen, Anduriel and Nicodemus prefer to operate behind the scenes. Also, Anduriel is able to hear almost anything uttered within hearing of a living being's shadow; with the exception of beings of Mab's caliber. Anduriel has therefore earned the title of Master of Shadows.

Anduriel used to be a captain in Lucifer's army after the Fall; he now leads the thirty Fallen who inhabit the coins.

Death Masks
In Death Masks, Harry Dresden meets Nicodemus Archleone and Anduriel for the first time. Dresden notes the way Anduriel moves in Nicodemus's shadow and sees some of what he can do.

Small Favor
In Small Favor, Harry Dresden and Nicodemus Archleone meet at the Shedd Aquarium in the entry hall, and is disturbed when he sees Nicodemus standing still while his shadow followed a shark. When they were alone, Anduriel began gliding around the walls, circling Dresden.

After Dresden reveals that at least one Fallen Angel is assisting Nemesis, Nicodemus is shocked and throws Dresden against the wall, demanding to know if he's lying. Anduriel emerges partially, opening "faintly glowing" green eyes over Nicodemus's own, and when Dresden doesn't fight back Anduriel speaks for the first time, commenting that Dresden at last showed some survival instinct.

Skin Game
In Skin Game, Harry Dresden comments that he has no idea what Anduriel can do because Nicodemus has never had to fall back on him. Kringle explains that Anduriel, while deadly in battle, is not a fighter by nature; instead, he functions as a spymaster for the Denarians, able to see and hear anything within range of a living being's shadow. He has to focus to hear or see what a particular person is done, and can come almost anywhere; the known exceptions being Demonreach, the Carpenter home, or in Mab's presence.

Word of Jim
The author has stated that Nicodemus has no other alternate form other than his animated shadow: "As far as he was [sic] having an alternate form, like the other Denarians do, no he just has his shadow go do things for him. You go relying on an alternate form to get things done, well that puts you in personal danger because you’re still inside there. Nicodemus is much more practical than that. ‘I’d rather stand over here and watch something else kill and actually get the work done.’ Unless it’s something cool like a Knight of the Cross, in which case he’s still got something to prove."

- Jim Butcher