Time to talk about linguistics as it pertains to literature — specifically Les Mis, and even more specifically Valjean and Javert. This is going to get pedantic and also very passionate, so buckle up, y’all, it’s gonna be a fun ride.
Several languages — French, Dutch, German, Russian, just to name a few — use two forms of address when speaking to another person (2nd person). French has a handy flowchart here which explains the difference pretty succinctly.
Basically, if a stranger bumps into you on the street, and you don’t want to get into a fistfight, you call them “vous.” But if you do want to get into a fistfight, you call them “tu.”
The nouns and verbs in French to describe this phenomenon, of addressing people in/formally, are tutoyer/tutoiement and vouvoyer/vouvoiement. The same way that gender is hammered into every single part of speech in French (even the chair has a gender, which, that doesn’t make sense to me but you do you, chair), so is in/formality. It’s not something they really emphasize in written literature because to them it’s just as natural as swimming is to a fish. For native English speakers, though, it’s a struggle to convey that cultural and linguistic difference without a couple paragraphs’ worth of explanation.
English used to have an in/formal dichotomy in the 2nd person address. “You” used to be the way a person addressed their teacher or king or possibly their parents, and “thou” was the way they addressed their friends, their children, and their underlings.
The interesting bit about English in/formality is that nowadays the “thee” form is only actively consistently used in places like Rite One of a Christian Protestant church service. We call God “thee” — we address Him informally.
(Yeah, there’s a theological reason for that, but I am not anywhere near qualified to answer that question.)
But in modern media depicting ye olde days, the “thee” form is used pretty haphazardly, addressing any old person any which way, when back in the 1600s that really wasn’t the case. If a princeling talked to some commoner on the street, the prince used “thee” on the commoner; if the commoner used “thee” back at the prince, he would probably have been beaten for the impertinence. There’s a reason all the best Shakespearean insults start with a “thou” — it’s purposefully conveying, through the dang pronoun even before you get to the good part of the insult, that the speaker is the hearer’s superior in every possible way.
With that in mind …
… Javert calls Valjean “tu” throughout the entire book — when he knows it’s Valjean he’s addressing.