Noah’s another typical minor Dickens character, in that he’s grotesque, absurd, and exaggerated. He’s skinny, lean, and eel-like, and has a taste for oysters and sneaking. Honestly, he kind of reminds us of Gollum.
But Lord of the Rings comparisons aside, Noah’s a pretty fun character. He starts out the novel as an apprentice in Mr. Sowerberry’s shop. He was a charity boy, and the other kids made fun of him. So as soon as Oliver arrives, Noah is pretty jazzed about having someone even lower on the social ladder than he is. Finally, someone he can dump on! Dickens takes this circumstance to moralize about how everyone likes to stomp on the people below them:
This affords charming food for contemplation. It shows us what a beautiful thing human nature is, and how impartially the same amiable qualities are developed in the finest lord and the dirtiest charity-boy. (5.26)
Noah’s obviously a source of comic relief and, like the Artful Dodger, the comedy comes partly from contrast: Noah’s absurdly scrawny, and Charlotte is burly and tough; but Noah bosses her around, and she submits like a lamb. Noah’s awfully fond of power, but too cowardly to do anything but sneak around, spy on people, and rat them out if he thinks it’ll be good for him.