The last wizard in London, a DCI for the Met (London Police) heading a unit of one specializing in magical crimes. He becomes Peter's teacher during the first book.
Gentleman and a Scholar: Being a full wizard in this universe means having an in depth understanding of "Newtonian magic" which, as the name suggests, is a system of magic with natural laws which is studied using scientific principles in the hope of advancing understanding of magic and/or figuring out and stopping the latest string of magical crimes.
Limited Advancement Opportunities: Has been stuck as a DCI for decades although the covert nature of his duties, and the self-imposed stagnation of The Folly, have probably contributed heavily to this, but strictly speaking in organisational terms he should have been made a Detective Superintendent in the service re-structurings of the 1980s and 90s.
Merlin Sickness: Nightingale was born in 1900, aged normally until the 1970s, and then for reasons that are still not clear began getting younger again. The effect is only on his biological age, however; his memory works normally.
The Obi-Wan: to Peter. Although he verges on Obsolete Mentor a couple of times, especially when it comes to modern police methods, and this is a particular bone of contention at the end of Soho when the issue of Inhumanable Alien Rights and due process through the courts, versus just killing sentient non-human possible criminals comes up.
Survivor Guilt: Nightingale is still haunted, even 60 odd years later, by his survivor guilt from WW2 and Ettersberg, the trip to the ruins of his old school (where they once taught wizardry) and the list of the fallen shows him to be still utterly broken by that last battle.
Constable Peter Grant
A young police constable saved from a career in paperwork after being found looking for a ghost who witnessed a magical crime by the last wizard in London whom he apprentices to towards the end of the first book in the series.
Alcoholic Parent: Peter's dad is a serious and habitual heroin addict. He isn't a bad parent but just a bit ineffectual, although Peter's mother being an Apron Matron probably means she did all the parenting stuff anyway. As of the end of Moon Over Soho he's clean, and remarks that of all the drugs he quit, nicotine was the hardest.
Britain Is Only London: Peter believes London is the only place worth being. Lampshaded in Moon Over Soho; Nightingale tells Peter that there's more to life than London, and Peter replies "People keep saying that, but I've never actually seen any proof".
Desk Jockey: Peter was about to be assigned to a career with the Met's Desk Jockey unit before meeting Nightingale.
Insistent Terminology: When Peter and Nightingale discover they're up against a black magician in book two, Peter points out that the term "black magician" is problematic, particularly since Peter is of African descent and is thus, in a sense, himself a black magician. Thereafter he uses variations on "ethically challenged magical practitioner" instead.
A world renowned gastroenterologist who also doubles as a cryptopathologist. He's a Scot from Oban who was raised a Presbyterian, but converted to Islam while studying medicine.
Admiring the Abomination: Most of the things he comes across are Nightmare Fuel, but he handles it all rather well and demonstrates a scientist's curiosity. Considering that he's been doing it for decades, his attitude is not all that strange.
Masquerade: He handles the stranger autopsies that go on in London as well as handling medical care for the Folly's residents.
Humanoid Abomination: Possibly. She creeps Peter out. Other supernatural beings and Toby are wary of her upon meeting her for the first time. Not even Nightingale seems to know WHAT she is. To put that in perspective, even the Night Witch—who survived the Nazis and went toe-to-toe with Nightingale—is cautious of her. Given what happened to Peter at the end of the first book, their caution might be justified. Peter believes that there's some relation between her and the Pale Lady
Lethal Chef: She favors making dishes popular a century ago. This suits Nightingale, but sometimes horrifies Peter. As of Moon Over Soho, she's been experimenting with new recipes leading to an attempt at Eggs Benedict that even Toby wouldn't eat. As of the fourth book, she's getting better thanks to the gift of a modern cookbook.
Older Than They Look: Looks like a young woman, but she's been at the Folly since she was a little girl which was around 1911.
Constable Lesley May
Peter's friend and fellow constable. After the end of book one she suffers an accident that destroys her face. The end of the second book reveals that she can do magic. She joins the Folly sometime before the third book begins.
Out of Focus: She only has a couple of scenes in book 2, but is back on the main roster for book three.
Scars Are Forever: Mr. Punch destroys her face. Despite her numerous operations, people are still shocked when they see her without her mask. Magic offers no cure either, which may be the reason she betrays Peter at the end of the fourth book since the Faceless Man was likely offering her a way to undo the damage.
Walking Spoiler: After the events of book one, pretty much everything she does has to come in spoiler tags. If you see a spoiler tag, it probably involves Lesley.
A Fire Investigation Officer and a reservist for the 4th Battalion, Parachute Regiment who leads the Folly's secret Armed Response Unit.
Badass Normal: He's a normal - albeit well trained and well armed - man who has to provide backup when a wizard needs a bit of help.
Stiff Upper Lip: Granted he's a veteran and has probably been dealing with the supernatural for a while, but he doesn't show any fear despite the threat of a nest of vampires, a murderous ghost, a rogue magician, a chimera, and a trio of succubi.
Professor Harold Postmartin
The Folly's archivist. He's based out of the Bodleian Library.
Really 700 Years Old: While there are quite a few people in the series who are Older Than They Look, Father Thames is close to about 2000 years old given or take a few decades. He was once known as Tiberius Claudius Verica making him a client citizen of the Roman Empire during the reign of Emperor Tiberius which went from 14 AD to 37 AD. Father Thames may in fact be the historical Verica who was a client king at this time.
The goddess of the Tyburn and Mama Thames' eldest daughter. She's dissatisfied with the current state of the supernatural community and wants to replace it with something more organized, including a government branch that handles supernatural matters.
Charm Person: She's strong enough that she makes Peter buy flowers, get on a train, and come see her despite his never having met her before and the fact that he was nowhere near her at the time.
Compelling Voice: She tries to use it on Peter to make him drink some water and end up under her complete control. It almost works.
Making a Splash: Being the goddess of a river, she has control over water. The first time we see her in the book she uses it for the rather mundane task of filling a vase.
Legacy Character: She is not the first spirit of the Tyburn, and Peter meets the ghost of the previous one in book three.
The Starscream: Mama Thames is quite happy with tradition and holding court out of flat, Tyburn is...not. Lady Ty has ambitions to sweep away the Folly and all the systems of "arrangements" and get everything out in the open. She also quite likes prowling the corridors of power at Westminster and Whitehall. Nightingale has said that when the eventual clash between Tyburn and Mama Thames comes then it might be an idea to take a holiday somewhere very far away.
Noble Profession: He was once a monk - presumably at Chertsey Abbey on the Oxley Mill River - and his own admission, he was a terrible one. He may have been a Dirty Old Monk given his love of women, the theatre, and Skinny Dipping.
Reasonable Authority Figure: He wants to end the conflict between the rival Thames factions before it turns into something worse. He also seems to genuinely like Peter.
The spirit of The Beverly Brook. Peter's on and off love interest. Likes to Drive Minis and act a lot more "street smart" than she really is.
Pretty Fly for a White Guy: A mild example of this, as Peter notes in book one, in that her river flows through some pretty upper-middle class area despite her acting all street and urban. This is reflected in her choice of car, which is the very middle class MINI.
Face of a Thug: Peter describes her as a squat, angry-faced middle-aged woman with lank brown hair who looked like she fought Rottweilers for a hobby, but she's a reasonable person who actually has a sense of humor.
Rank Up: Promoted from Detective Sergeant to Detective Inspector at some time between the second and third books.
Reasonable Authority Figure: She more or less takes Seawoll's place during the second book while he's recovering from the incident in the first book. She's less antagonistic about magic, but still wants all the cases to be solved with evidence that can actually be presented in court.
Family, Friends, and Miscellaneous Spirits
Richard 'Lord' Grant
Peter's father. He was a famous trumpet player in his time and on the verge of becoming a legend until heroin addiction ended that chance. It's hinted in the second book that because he was a victim of the jazz-vampire/succubus Simone that the addiction wasn't completely his fault.
Career Resurrection: An In-Universe example. He switched instruments and formed a band with some secondary characters from the second novel. As of the fourth, he's considering dental surgery so that he can play the trumpet again.
Cool Old Guy: He's not quite The Obi-Wan, but he will hand out advice to his son. Being a rather famous jazz musician - at least to those who know jazz - also helps. In fact, his knowledge of jazz proves quite helpful in the second book.
Functional Addict: Heroin destroyed his teeth and thus his embouchure which meant he could no longer play the trumpet with the same amount of skill. He was receiving heroin thanks to a doctor who was his fan. As of the second book he's given up heroin.
Ray Charles: After hearing him play Charles said, "Lord, that boy can play". 'Lord' ended up becoming Grant's nickname.
Education Mama: She wanted Peter to be something more than a police officer. She actually finds that his working with magic is a more acceptable career than being a constable and tells certain people that he's a witch smeller.
Lethal Chef: She's not a bad cook, but she loves her spices. Given the number of supernatural beings in the series, there's a chance that we might find out if her cooking is literally Too Spicy for Yog Sothoth.
Out Grown Such Silly Superstitions: Given that the series takes place in what's more or less the real world, most people don't believe in the supernatural and those that do are seen as superstitious or ignorant. This led to a bit of initial Arbitrary Skepticism on Peter's part when his mother attacked Simone and called her a witch. Peter didn't believe that Simone was around when his parents first met i.e. before he was born. It turns out that his mother was right. Simone is an ageless being and has been feeding off of jazz musicians since World War II.
A young man Peter meets while investigating a murder in the third book. He proves to be more than he appears and introduces the Peter to London's supernatural underground.
Nature Spirit: Specifically a wood nymph from a London Plane Tree.
The Faceless Man
The ethically challenged magician introduced in the second book and the closest thing the series has to a Big Bad so far. He's the second man to hold the title. The first - Albert Woodville-Gentle - was likely his teacher.