Who is Jack Kearns from The Monstrumologist and what is their importance?

Doctor John Kearns (Jack) is a surgeon, but as Warthrop notes, he is something all together more sinister as well. Having hunted Anthropophagi, Kearns has experience in the matter and yet, he is also a dangerous man. When Kearns arrives, he appears jovial enough, charismatic, and overall genuinely kind. However, he also seems to have an odd sense of humor, and even Warthrop seems wary of the man. In time, Kearns shows his jovial nature can turn quickly into malevolent joy at others' expense. Kearns is not kind, or caring, but reveals himself to be a void of emotion. He has little sympathy for anyone, including young Malachi, and his demeanor rapidly changes to take charge of the Anthropophagi hunt.