Sergeant Zuli is a member of the militia of the town of Zumzum, first encountered here ✣ . He's an old hand in the military with the scars to prove it, notably what looks like a prosthetic left ear and some facial scrapes.
The good Sarge serves to explain to the naive Agatha, accompanied by Thundering Engine Woman, some realities about life in the boonies, for example the local attitudes toward Jägermonsters and the Heterodynes. Agatha can't figure out why bad stuff doesn't happen to the people of Zumzum when they string up Da Boyz, who after all are Jägers and therefore in the employ of Baron Klaus Wulfenbach -- or so she thinks, not yet grasping the concept of wild Jägers (reasonably enough). Zuli explains that Zumzum is so far out in the sticks that the Baron has better things to do than interfere in the way the town polices itself, and goes on to point out that the townsfolk have pretty good reasons for their attitudes. Simply put, House Heterodyne and their minions (i.e., Jägers) don't have a good reputation in places like Zumzum. This gives Agatha something to think about...
Shortly afterward, Zuli is on duty ✣ when Jenka and Füst come calling, and narrowly prevents a trigger-happy underling from launching an attack on them that would probably lead to the leveling of Zumzum.