A 300 year old exiled dragon princess from the Inland Sea. Like most dragons, she's somewhat vain, but has a good heart. Her home was destroyed by the witch, Civet, and for the course of the series, is trying to find a way to restore the waters to the Inland Sea. Shimmer was exiled from her clan by her older brother when she refused to relinquish her mother's dream pearl (a potent magical artifact) to him.
The Unfavourite: Thorn manages to displease Shimmer after Indigo joins them in their quest to restore the Inland Sea. This causes Shimmer to start favouring Indigo.
An anthropomorphic monkey based off the Monkey King from Journey to the West. He's notorious for being a troublemaker, and was imprisoned under a mountain for quite a long time by The Old Boy, one of the Old Masters. He considers the Old Boy to be his master, and is one of the few individuals he treats with the utmost respect. Monkey has amassed a vast repertoire of magical abilities and skills, and is a force to be reckoned with. He's cunning, sneaky and tricky and acts as Shimmer's foil.
Carry a Big Stick: Monkey stole a magical pole from the High King of Dragons, and it can change from the size of a needle to several dozen feet long in an instant. He keeps it tucked behind his ear when he's not using it.
An orphaned 13-year old girl who was brought up in the Dragon King's undersea palace as a servant. Like Thorn, she was mistreated for much of her childhood, but unlike Thorn, it's made her cynical and bitter. Because of the way she was treated by the royal dragons, Indigo harbours a kind of resentment towards them, especially the aristocracy. The only remotely idealistic thing about her is her hope of one day being able to visit the Green Darkness, a village inside a magnificent forest. Her parents had come from the Green Darkness before they came to live (and die) in the dragon palace, and Indigo carries on certain customs from her ancestral home, despite never having visited it. She wears her hair in traditional spikes, and dyes them a dark blue.
Improbable Hairstyle: Indigo's trademark hair spikes, which are the traditional hairstyle of people from the Green Darkness. Given that she's lived on the ocean floor her whole life, she has to grease them heavily to keep them that way.
Morphic Resonance: When Indigo is transformed in to a dragon for the sake of convenience, Shimmer botches the spell, and Indigo keeps a ridge of blue spikes along her back. Indigo decides that she likes this defect, and requests that Shimmer add it in on purpose the next time she gets transformed.
The Smart Guy: Despite not being the devious trickster Monkey is, she often comes up with intelligent plans and ideas to thwart people who stand in her way.
Tragic Dream: She's built all her dreams around one day going to live in the Green Darkness, but with no realistic way of actually getting there. On top of that, her expectations of it were so overblown that it would have been hard to meet them even if she made it. The absolute worst part is that in actuality, the Green Darkness is suffering from some pretty rough times under the Butcher's reign and is far crappier, even, than most people's actual memories of it.
A witch who lived in a village called River Glen over a thousand years before the start of Dragon of the Lost Sea. A powerful river spirit, known as the King Within the River, demanded her as a bride when she was sixteen, and drowned her so that she could live with him forever under the waters. Because of this, she's eternally preserved in her sixteen year old state. Over the course of a millennium, she slowly learned magic from the King Within the River. She uses this magic to transform him into a rock, and escapes from what had been a thousand year-long prison sentence. Before the events of the first novel, she destroys Shimmer's former home, the Inland Sea.
Disproportionate Retribution: Upon escaping her arranged marriage (after a thousand years, mind you), and seeing her former home had industrialized, Civet is overcome by loss and decides that dragons are responsible. She destroys the Inland Sea where the Inland dragons live, by taking away all the water, and then uses the water to destroy River Glen, her former village.
Late-Arrival Spoiler: Civet is the villain of the first novel, but ends up allying herself with Shimmer and the gang at the end of Dragon Steel. Depending on what edition you're looking at, the covers of later books might even spoil this for you completely.
You Can't Go Home Again: Considering she's been underwater for a thousand years, everyone she knew is dead, and even her home has been completely industrialized to the point that she can't recognize it anymore.
Shimmer's selfish older brother. At the start of the novel, he is the King of the Inland Sea, and the one who exiled Shimmer. He wishes to take Shimmer's dream pearl for himself, and be the ruler of the world.
Black Magic: The Boneless King is a very potent magic user.
Non-Human Sidekick: In spite of the fact that he wants to destroy all living things, he actually has a pet dog named Snowgoose.
Obfuscating Stupidity: After he takes over The Butcher's body, he has to pretend that he's still The Butcher, in order to keep his subjects from becoming suspicious and overthrowing him. This includes hiding his magical abilities by having an incompetent court magician cast spells, while performing magic behind the court magician's back and making it look like the magician is doing it.