The October Daye series is richly described and also well-populated with a variety of characters.
The Firstborn (Serious Spoiler Warning)
The Firstborn are the sons and daughters of the Lord and Ladies of Fairy: Oberon, Maeve, and Titania. Maeve's children are hot, Titania's children are cool, and Oberon's children are heroes (a bit ironic, given that Maeve is the Winter Queen, and Titania the Summer). They are as powerful compared to their children as the Lord and Ladies are compared to them - practically gods. Most are the progenitors of one (or possibly more) fae races. Who they are counts as spoilers, so beware unmarked ones. They were given real names by their parents, but took titles as a warning to their children.
AmandineToby's mother, the first Dochas Sidhe.
The LuidaegNot a sea witch, the Sea Witch. The mother of all Roane ... and Selkies. Maeve's daughter - possibly the only remaining one.
Blind MichaelLeader of the Wild Hunt. The Erl-King. Son of Maeve.
AcaciaBlind Michael's consort, the first Dryad and Luna's mother. Daughter of Titania.
Eira RosynhwyrDaughter of Titania. Firstborn of the Daoine Sidhe. The Luidaeg's mortal enemy.
Black Annis and Gentle AnnieDaughters of Maeve, sisters of the the Luidaeg. Killed by Titania's children.
Amorica and EltonTwins. Firstborn of the Tuatha de Dannan.
Arawn of the White StagA wild Firstborn who created the deep realm of Annwn.
Shadowed Hills is the knowe held by Sylvester Torquill, who is one of the most beloved nobles in fae society. He runs his household with kindness and love, and is pretty much fatherly toward changelings, where most full-blooded fae are disdainful toward fae with human blood.
Sir October Christine DayeThe protagonist of the series.
Connor O'DellA Selkie, old friend and flame of Toby's.
EtiennePureblood Tuatha de Dannon. First knight of Shadowed Hills. Hidebound, traditionalist, inflexible - but also decent, kind, and determinedly loyal. Toby's grudging trainer, and eventual friend after Ashes of Honor.
GriannePureblood Candela, a species of fae with accompanying illuminating Merry Dancers, which can help teleport, scout, and many other useful things. Third-in-command of Sylvester's knights. Pretty taciturn.
JinPureblood Ellyllon who works as Shadowed Hills's healer.
Duchess Luna Torquill
QuentinA Daoine Sidhe teenager, in blind fosterage until age 21.
Rayseline TorquillSylvester and Luna's only child.
Duke Sylvester Torquill
Melly and OrmondHobs (who love cleaning) - in charge of Sylvester's cleaning staff.
The Tea Gardens
LilyUndine Lady of the Tea Gardens.
MarciaA quarter-blooded changeling who needs faerie ointment to see Faerie at all. Lily took her in when most of Faerie wouldn't. As of One Salt Sea, she is the seneschal to the Count of Goldengreen - first to Toby, then to Dean Lorden.
Walther DaviesA Tylwyth Teg who teaches chemistry at UC Berkeley.
A small independent County, home of A Local Habitation Software.
January O'LearyCountess of Tamed Lightning, niece of Sylvester Torquill, daughter of September Torquill. Half Daoine Sidhe, and like many blood mixes, slightly insane.
April O'LearyJanuary's adopted daughter. A dryad who lost her tree, January worked the last still living bits of wood into the circuitry at Tamed Lightning, and made her a cyber-dryad. She inherits Tamed Lightning after her mother's death.
Alex and TerrieA brother and sister pair of changelings that work at ALH. Also essentially walking spoilers.
The Court of Cats
The Court of Cats has no precise location, and is connected by the Shadow Roads, accessible only by the Cait Sidhe and perhaps by actual cats.
TybaltThe current King of Cats of San Francisco.
RajRoyal Kitten, being groomed for succeeding the king when Tybalt is ready to retire. He is the first born in sixty years, so he is considered very, very precious. He is deeply devoted to Toby, who has rescued him from several terrible situations since they've met. He is Samson's son, Tybalt's adopted nephew, Quentin's best friend, and Toby's unofficial squire. Dating Helen, a half-Hob who helped him when they were both taken by Blind Michael in An Artificial Night.
JulieThis commoner Cait Sidhe was one of Toby's oldest friends. She is now a former friend, due to Julie holding a grudge that Toby got her human boyfriend killed. It wasn't quite as cut-and-dry as all that, but Julie doesn't want to see reason.
SamsonSamson is Raj's father but not related to Tybalt, who once regrets letting them remain with Raj after Tybalt claimed him.
Home: a halfway house for down and out Changeling children. Since humans were weirded out by changelings (or the Changelings themselves couldn't fit in with human society) and the fae disdain them, Home was a place where changelings could be counted on to look out for each other to a degree. It burned to the ground early in the series.
DevinOwner/operator of Home. He is pretty much the Fagin of the operation. Also Toby's first love, and lover. Part Lamia, part other things - but not pureblood.
DareA Tylwyth Teg changeling, sister of Manuel.
In and around San Francisco
Danny MacReadyA local Bridge Troll who drives cabs. Toby rides free due to having saved Danny's sister.
May DayeMay is, to all intents and purposes, and legally speaking for the mundane world, Toby's twin sister. The truth of her existence is a bit stranger. Specifically, she's Toby's Fetch. Dating Jasmine ("Jazz"), a Raven-maid.
The Brown FamilyMitch and Susan Brown are a changeling couple and two of Toby's oldest friends. They have five children: Cassandra, Jessica, Karen, Anthony and Andrew.
Officer Michael Thornton SFPDHuman police officer. Helped Toby when she first broke free of the fish curse, and later followed her to Annwn in Ashes of Honor.
CliffToby's former human lover, now remarried to a human woman.
GillianToby's quarter-fae changeling daughter by Cliff.
BridgetProfessor of Folklore, UC Berkeley and former human lover of Etienne. She is also mother to Chelsea, who Toby turned completely fae-blood as of Ashes of Honor.
Cagney and LaceyToby's cats. As such they also are subjects to Tybalt's local Court of Cats.
SpikeA Rose Goblin (a magical creature that looks like a cat made from a rosebush) that Toby accidentally adopted when she named him.
There are four realms of Faerie - Land, Sea, Air, and Fire. Since Toby is a Land fae, the books primarily deal with Land fae and their society. However, Connor, as a Selkie, is part of the Undersea, and through him and the Luidaeg (the Sea Witch), Toby comes into contact with the powerful Duchy of Saltmist, which runs up most of the California seaboard.
Duchess Dianda LordenMerrow (basically mermaid with storm powers - also the most common and powerful of the Undersea species - called by Toby the Daoine Sidhe of the Undersea). Regent of Saltmist. Incredibly powerful, incredibly hot tempered, incredibly awesome. On land, likes to fight by jumping at her enemies in her two legged form, then transforming and using her very muscular tail to beat her opponents senseless.
Patrick LordenPureblood Daoine Sidhe. Was a landless baron until he married a Duchess of the Undersea and renounced his title to play ducal consort. Friendly, levelheaded, and a good balance to his wise but fierce wife.
Dean LordenOne of their two sons. His brother Peter inherited his mother's Merrow form, while he inherited his father's Daoine Sidhe form (but with webbed hands). Toby transferred her title of Count of Goldengreen to him in One Salt Sea.
Simon TorquillTwin brother of Sylvester. His plot to kidnap Luna and Rayseline is the reason Rayseline became Ax-Crazy, and the reason Toby lost 14 years and her relationship with her lover and her child.
Oleander de MerelandsSimon's lover, an altogether nasty piece of work. Half Peri, half Tuatha de Dannan, all evil.
Evening WinterrosePureblood Daoine Sidhe, Countess of Goldengreen, champion of Toby when she brought the murderer of her sister Dawn to justice. Helped Toby get back into human society after returning from her accursed exile. Her murder kicks off the series.
Treasa RiordanPureblood Daoine Sidhe. Either insane or insanely ambitious. Duchess of Dreamer's Glass. Has a bunch of air faery guards called the Folletti.
Li Qin ZhouShyi Shuai - luck reading species. Wife of January O'Leary. "Temporary" regent of Dreamer's Glass after Riordan's...unfortunate "accident."