The main character. At first an ordinary eleven-year-old kid living in New York City, he discovers the Underland when he follows his baby sister down a vent in their apartment building's laundry room and learns he's the prophesied Warrior.
A Boy and His X: At the end of Gregor the Overlander, he bonds with the bat Ares.
Lampshaded in Gregor and the Code of Claw, when he realizes that if his rager skills fail him, he's just a twelve-year-old kid who's had a few sword lessons, and therefore in big trouble.
The Berserker: In Gregor and the Prophecy of Bane, he learns he's a "rager" a person with highly developed warrior skills, a natural-born killer. Meaning he has a natural capacity to go into this state when his life is in danger. It's not always voluntary, which is really bad for a character who normally hates to kill.
Blessed with Suck: Turns out being the Warrior of the prophecy isn't much fun for him. At the end of the series, he is warned that with his rager abilities it will be much easier for him to kill people, so he'll always have to keep an eye on himself.
The Call Knows Where You Live: He never wants to fulfill the prophecies that Sandwich set down for him, but they always find a way to rope him in. Particularly in Gregor and the Curse of the Warmbloods, his Grandma tells him "You can run away, but the prophecy will find you somehow." A bit later his mother is infected with a deadly plague forcing him to go after the cure. The call metaphorically hits him right where he lives.
Ripred's "escort" for him is a much more literal example from the same book.
Covered with Scars: By the end he's racked up an impressive total. After his fight with the Bane, he basically gives up the idea of even coming up with an excuse for them.
Dark Is Not Evil: He wears black armour during the final battle, and his bond is black as well.
Death Is Such an Odd Thing: The Kill 'em All ending leaves him in a state of emotional distress about many characters, many of whom were absolute jerkasses toward him. Particularly in Gregor and the Code of Claw, when faced with the Prophecy of Time that foretells his own death.
Disappeared Dad: His father in Gregor the Overlander, vanished when he was eight. They find him though.
Promotion to Parent: With his dad missing, his mom working, and his grandma's dementia, he starts out with a lot of weight on his shoulders. Things don't get much better when he has the Underland to think about as well.
You Can't Fight Fate: Brought home in Gregor and the Curse of The Warmbloods when his mom contracts the plague; he acknowledges mentally that there was no other way to ensure the prophecy would happen the way it needed to.
At the start of the series, their father has been missing for over two years.
Adults Are Useless: The parents are not completely useless, and never by choice, but they are rarely able to help Gregor with his unique problems. Averted in Gregor the Overlander when the dad manages to steer them back to Regalia.
Disappeared Dad: The father in Gregor the Overlander, vanished when Gregor was eight. They find him though.
Shipper on Deck: The mom who secretly approves of Luxa, because she's "got attitude."
An older widow who lives in the same apartment building as Gregor's family.
Maybe Magic, Maybe Mundane: She tends to send just the right objects at just the right times and who gives tarot readings. Gregor at one point wonders if she can see what he needs in her tarot cards, and given that psychics exist in this series, he could be right.
Nosy Neighbor: A well-intentioned and not especially annoying version, but any questions are awkward when you don't know have a good explanation.
Secret Keeper: Becomes this for the family starting in Gregor and the Marks of Secret.
Aerith and Bob: The humans have both typical English names — Henry, Howard, York, Susanna, Judith — and more fantastic names like Solovet, Nerissa, Vikus and Mareth. Lampshaded when Gregor is introduced to – Henry, he almost laughs that "among all these strange names, there's a Henry".
Bat out of Hell: Averted, as the bats are the humans' most valuable allies.
Bond Creatures: The humans and the bats are the only species with this. Until Gregor and the Code of Claw.
Call a Rabbit a "Smeerp": The assorted oversized creatures of the overworld are given simpler names, allegedly by the people who live there. (Rats are known as "gnawers", spiders as "spinners", and so on.) This is what the creatures of the Underworld actually call themselves, just translated into the nearest thing in English. Humans have one of these names too among the Underworld creaturesnote "killer", but they don't like to hear it.
Deadpan Snarker: Seems to be an inborn trait of the rats, who are also some of the few underlanders to use informal language.
Twitchtip: (when Photos-glow-glow "can't understand" boots): Allow me to translate. She said If you don't stop you incessant bable that big rat sitting in the boat next to you will rip you head off.
Evil Albino: This could also apply to some of the humans in the series, but every single Underland human is a violet-eyed albino and a majority of them aren't that despicable.
Evolutionary Stasis: Averted in that the Underlander humans' eyes turned purple and their hair turned a very light blond. Although how living under ground could cause a change in melanin levels that quickly could be an example of artistic license.
Even though the crawlers/cockroaches, gnawers/rats, spinners/spiders, fliers/bats, etc. that coexist with humans in the Underland are not human, they are sentient and treated as full characters on the same level as humans. Prejudices held among human characters towards these species are even treated as equal to any intra-human bigotry.
The bats, humans, and mice are allies with each other, and hate the rats, who hate just about everyone but especially the humans and mice. The insects pretty much hate all the mammals. The spiders are willing to play both sides, and the cockroaches are considered stupid.
Humans Kill Wantonly: The giant, intelligent rats are called "Gnawers", bats are "Flyers", mice are "Nibblers", etc. Humans are " Killers", a moniker they picked up after they nearly drove a population of moles to extinction in order to take their land. Not that anyone would call them that to their faces, of course.
Lazy Bum: The fireflies. Mareth describes how he once saw two fireflies try to fight to the death over a piece of cake, only to accuse the other of cheating and resort to sulking.
The Nose Knows: The rats demonstrate this quality in their first appearance by accurately calculating what Gragor and Boots ate for dinner hours earlier right down to the tiny bowl of greens. They also are shown to be able to estimate human emotions and navigate and fight in complete darkness.
Old Shame: invoked In Gregor and the Code of Claw, it's revealed that Bartholomew of Sandwich resorted to poisoning the moles to get their land. It was thought they were all killed by this tactic, and it poisoned everyone else's opinion of the humans.
Unable to Cry: Gregor really starts warming up to her when she tells him that she has not cried since her parents' deaths. When her cousin Henry betrays her at the end of Gregor the Overlander, she goes into a catatonic state of sorts, and it seems like she still won't cry - until she sees Vikus.
Nice Guy: Would much rather talk through differences than fight over them.
No Accounting for Taste: With Solovet: she's a ruthless general willing to resort to almost any tactic to win, he's a pacifist at heart who always tries the diplomatic option first. When Gregor comments on how odd it is that they are married, Vikus admits it has always been somewhat of a puzzle to them as well.
Fair Weather Mentor: He could fit into this, particularly in Gregor and The Curse of the Warmbloods.
Jerk with a Heart of Gold: He's an antisocial semi-loner with only a small band of outcasts around him, and doesn't respect anyone unless they earn it from him. He has his moments, such as in Gregor the Overlander comforting Gregor after one of the quest members dies and he feels it's his fault, but in Gregor and the Code of Claw, we learn he had a family that drowned in an event described in Gregor and the Mark of Secret. He had a daughter, named Silksharp, that liked to do math puzzles and was apparently not very strong-bodied. Lizzie, the middle child of Gregor's family, reminds her of him. One of the heartwarming moments of the book is him comforting Lizzie in the middle of the night after she has a panic attack.
The Nose Knows: She has such a sensitive nose that she is called a "sent seer." Among other things she can detect the sent of a rager, newly hardened volcanic rock, a whirlpool, and the color of Boots' shirt from out side the castle tower Boots is in.
Establishing Character Moment: Interestingly enough, he gets one after his initial introduction. We first meet him as a baby, whose cries for his mother make it impossible for Gregor to kill him. What could be more innocent? Well, in Gregor and the Marks of Secret, we learn he killed his devoted caretaker. Still, he said it was an accident, and he's so big he might not know his own strength .. he tried to eat him to cover it up?
Woobie, Destroyer of Worlds: His father killed his other children so Pearlpelt could have more milk and grow stronger. His parents killed each other in a fight, and he saw his mother lying dead with her innards spilled over the ground. To make matters worse, almost all the humans shun him because he's the Bane, and many of his fellow rats honor him and want him to be their king. Eventually, he goes completely off the deep end, becoming an Evil Albino and a great Hitler allegory.
Failure Knight: He shouldn't have listened to his mother and let the flood gates open so that everyone would drown.
My God, What Have I Done?: He has this when while trying to drive the rats out of the Garden of the Hesperidies, he permanently floods the garden, destroying the apple trees, drowning countless rats, bats, humans, and even the rat pups who had been taken into the cave to escape the fighting, leading to him fleeing Regalia to live in the jungle.