Who comes from the sewer, besides the Teenage Mutant Ninja Turtles and the Penguin? Arthur, that's who. When we first meet our main man, he is climbing out from a drain cover and then flying through the night on a pair of wings invented just for him. So we're going to go ahead and say that Arthur is pretty courageous. But as is often the case when it comes to bravery and risk taking, this has its ups and downs.
Arthur doesn't seem afraid of heights or much else, really. When his underling friends are trapped in the Cheese Hall, he tries to find them, exploring every bit of the place, including the dungeon. To be clear, this isn't some frilly and pillowy dungeon or anything, either—it's as scary looking as a room by its name is supposed to be: "It was very dark down those steps, he thought nervously. Then he swallowed and started down" (20.27). But even though the dungeon scares him, Arthur goes down there anyway to try to find his friends.
He does have the sense to worry when he's in a bad situation, though. So, for instance, when the police turn him over to Snatcher's custody, he sort of freaks out: "The thought of trying to escape from the Cheese Hall again filled him with despair. And what on earth would they do to him once they got him there?" (28.55). Luckily Arthur doesn't give into despair, and he's inventive enough to get out of most messes.
It's a good thing Arthur has a good head on his shoulders, too, since this guy is all about having adventures. Growing up underground with Grandfather must not have satisfied his natural curiosity, since Arthur is keen to explore the above world. When he first spots the cheese hunt, Arthur is thrilled to investigate it: "Here at last was a chance for some real adventure" (3.23). Of course, Arthur gets a bit more than he'd bargained for when Snatcher captures him and takes away his wings. But them's the breaks when it comes to adventuring, we suppose.
Plus, it's not like Arthur's bravery never borders on stupidity or anything like that, because it totally does. When he spots an opening to sneak into the Cheese Hall, he takes it—and ends up locked inside the Cheese Hall, surrounded by bad guys. Maybe a smidge impulsive there, kid. Even stuck in this bad situation, though, Arthur keeps coming up with places to hide until he eventually manages to escape.
Basically, Arthur isn't one to back down from a challenge, and he's also not one to run away from a scary situation. After he's rescued from the Cheese Hall dungeon, he intends to go back to finish things. The Great One is about to devastate the town of Ratbridge—which Arthur doesn't have any particular loyalty to, but he wants to make things right. When Grandfather tells him to be careful, he responds:
"I have to go back. I am not sure what's going to happen but I need to be there." (47.30)
That's our boy. And this little response of his brings us to our next point about Arthur: He isn't just brave with some pretty sold thinking skills—he also is quick to care.
Roses are red, violets are blue, Arthur is nice, and you should be, too. We see Arthur acting quite considerately of other's feelings, which is interesting since he basically grew up isolated from society. When a party is about to set out to investigate the Cheese Hall, leaving the mini-critters behind, Arthur asks, "Should we leave them anything to eat?" (16.125); he also consoles the mini-boxtroll, Match, who is freaking out after the other boxtrolls have been kidnapped, saying:
"Don't worry, Match, we'll get the others back. It's all going to be all right." (15.67)
Way to take a moment for the little guy, Arthur. He's a generous kid, too, offering to share his mulberry cake with Marjorie, despite her declaration that he "'wouldn't be offering to share it'" (14.78) if he knew how good it actually was. At this point we're guessing that Grandfather raised Arthur with good manners and instructions to be kind to others, a principle which Grandfather himself has modeled all these years by loving Arthur as his own, even though they aren't blood relations. Grandfather found Arthur as an abandoned infant, and has stuck with him ever since.
Even though Arthur can't always keep himself out of trouble, he tries to help others when he can. When everyone is evacuating the lab before it blows near the end, Arthur remembers the tiny mice he'd seen in Snatcher's room. Does he know who these mice are? Does he owe them anything? No and no, but he dashes in to rescue them anyway. Turns out they're the missing rats from the ship, shrunken after being captured, and thanks to Arthur they're now safe.
For a young-ish kid (we peg him in the eight to ten range), Arthur sure comes up with a lot of smart ideas. Like when their party goes to investigate the Cheese Hall, but can't get in, Arthur suggests, "'We just need someone to keep an eye on the entrance […] How about we rent a room and set up watch?'" (18.35). Well done, kid.
Arthur's also pretty curious in general. When he encounters his first freshwater sea-cow, for instance, he "stared in awe at its enormous black-and-white body floating beneath the water" (9.10). His openness to this new creature, as evidenced by the "awe" which he greets it with, is similar to the open-mindedness that enables him to think of innovative solutions to problems. Arthur is ready to meet the world as it comes his way.
He is capable of making logical leaps, too. So when Willbury is ruminating over all these new miniature creatures he's never heard of before, Arthur says, "'I suppose there are different types of creatures in different countries'" (14.3). We're not calling the kid Einstein or anything, but we are noting his ability to take his own experience of seeing a freshwater sea-cow for the first time and use it to draw some logical conclusions about the way the world works. Remember: Arthur's basically spent his entire life underground, so it's not like he's well-traveled or anything.
It's this combination of open-mindedness and logic that enables Arthur to come up with savvy solutions to problems time and again, be it managing to steal Snatcher's keys before Arthur is imprisoned in the dungeon, rebuilding the motor to his wings, or any of the other binds Arthur finds his way into—and then out of.
The biggest example of this, though, is probably the showdown with the Great One, when Arthur comes up with the plan to use a giant magnet to neutralize Framley in his iron armor. Arthur sure knows his science fundamentals, and this out-of-the-box idea ends up saving the day. Marjorie characterizes Arthur as "'sharp as a knife'" (49.70), which is pretty high praise coming from her. She even asks him to be her helper in her new invention endeavors, saying, "'I need a bright assistant'" (55.93). We'd say Arthur definitely fits the bill.
Because Arthur grew up underground, with Grandfather as his only real companion, he's not much of a people-person. So though he's curious about the aboveground world, he doesn't exactly know how to handle himself in it. When Willbury takes Arthur to the market to buy groceries, for instance:
Arthur was astonished. He had never been aboveground in the middle of the day before. He never dreamed that there could be so many people in the world. Suddenly he felt rather frightened. (11.82)
Sounds a lot like culture-shock, poor kid. And the thing is, that for all of Arthur's adventurousness and sound thinking, his isolated background leaves him quite uncertain about two specific things that the rest of us might take for granted: friends and women. Walking through the market, Arthur has his first glimpse of kids plating, and it gives him a little case of the feels:
Some of them were kicking about a leather ball the size of a cabbage, while others were chasing each other or fiddling with sticks in puddles. Arthur felt a little jealous at the easy way they laughed and spoke with one another. (12.1)
Sad face. Grandfather's great and all, but in just seeing other kids, Arthur immediately feels a sense of loss about his own life (otherwise he wouldn't feel jealous). Though it's a bummer for Arthur to realize that he's missed out on having other kids as friends during his short life, Willbury doesn't let him get away with this pity-party for very long, responding to Arthur's complaint that he doesn't have any friends by saying, "'I think you do! What about Fish… and Egg and Shoe… and Titus… and me?'" (12.7). That gets a smile out of Arthur, for sure.
The fact that Arthur is unfamiliar with ladies may account for his uncertainty regarding Madame Froufrou. She looks "oddly familiar" (13.6), but Arthur doesn't realize that she's actually Snatcher in women's clothing until he finds the clothes in Snatcher's desk.
At another point, Arthur is left alone with Marjorie, which leads to this realization: "This was the first woman he had ever spoken to and he felt a little bashful" (14.85). It's almost cute if we don't consider that this is the result of a lifetime of isolation underground. Luckily, though, Arthur gets over his shyness and goes on to become Marjorie's friend and helper.
By the book's end, Arthur has become friends with the crew of the ship, the various underlings, and humans like Marjorie and Willbury. They shower him with friendship, helping him and Grandfather sort out their new living situation. And Kipper gives Arthur a mini ship in a bottle as a token of friendship, leading Arthur to have an emotional response: "Arthur could barely speak, he was so moved" (54.79). Surrounded by new friends, and no longer exiled to the underground, Arthur seems ripe to blossom into young adulthood. Yay.