He is a stupid dick.
Haven’t read the comics, so this is a genuine guess. But i think his books are undercover tails of Viltrumite Empires and the intricate details about it and how Mark can protect Earth and defeat the Viltrumite empire as well as the rules and culture of Viltrum.
In every Invincible comic strip that i have seen being posted on the subreddit, Invincible is always suffering or crying.
To weaken Earth’s defenses so that Viltrumite Empire can take over when the time comes.
Nolan even seems quite respected amongst the Viltrumites. It must be that he is one of the strongest amongst them.