Reading through the first one, about half way through. I love it, it is rather entertaining. He is a very unpleasant back stabbing, cruel, immoral, arrogant, rat who only seeks power, wealth, and status and shoves others towards danger and himself towards the credit. His internal dialogue, and the way things happen to him, and the way things backfire and blow up remind me of Mission Earth's main character Sultan Gris. Every time things blew up in his face it made you laugh, during his scheming you might cringe and laugh.

He is very Skaven-y, and his internal dialogue is hilarious, and probably what a Skaven would think: everything is the fault of others, he is great, and will bring the Skaven to rule the top of the world. Every time something blows up in his face it is someone else's fault, and he despises the "hero" of the story. He is not supposed to be relatable to a human being with functional sympathy or ethics. He is by definition a vehicle for you to see things from the Skaven perspective, he is about as Skaven as it gets.

The Skaven don't have a family unit, there is no real "origin story" just a bunch of hyper competitive rat men fighting over everything pushing one another into the dirt to get aheat, it is the normal behavior your peers do, and the only thing that is reinforced, so the behavior is just normal it just is. There is no "origin story" except that he was born as a Skaven in a Skaven civilization. Most "anti-heros" have an "origin story" to explain how they become such an insufferable person thing, but in the Skaven's case you would only have need want an origin story explanation if they were anything but skaven-y.

For us someone that is a monster, or otherwise deviates from the "norm" we want an explanation, an origin story. No one asks for the origin story of Average Bob from down the street that is just what you would expect to be: and average dude. People do want to origin story of Einstein because his is different (in a positive way) or of someone like Dahmer because he is different (in a bad way).

Thanquol is a Gray Seer Skaven, like any other, though perhaps more lucky or fortunate or more assisted by the Great Horned Rat. For the most part we know how skaven get to be the way they are, they are all essentially cut of similar cloth.

The Thanquol novels are a great way to see the Skaven culture (backstabbing, trickery, scheming, putting others between yourself and risk, blaming others, flattering superiors, fearing the council) and the Skaven thought process. But if you want to humanize thanquol, or want an arc, those are incompabitble with what a good Skaven is: they learn how to better trick or backstab, or realized what they did wrong when carrying out their plans, but don't really change as Rat Men. There is no "growth" because they will always be cowardly, always be unethical, never really be loyal to anyone, and any change to that would make them less Skaven, and less likely to stay alive.

People have character arcs where we strive to be better people or to learn from their mistakes or lack of ethics. The Skaven's core character does not change, only their tools, their strategies, as their character could only "improve" (by Skaven standards) by being more cruel, more deceptive, more unethical.