"Earnest, learned, prone to jump at loud noises."
The Haunted Doctor is a doctor and revolutionary, originally from the Surface, who gave one of his eyes to a spider-council in exchange for knowledge. The visions the council shared with him led to his joining the ranks of London's anarchists. He rose high enough in the ranks to learn of the anarchists' end goal, the Liberation of Night, and thought it was the only path forward.
Meanwhile, the Haunted Doctor also rose high in the medical profession, and had several opportunities to kill patients the revolutionaries wanted dead. Eventually, he was ordered to kill one of the Calendar Council, likely March, and after killing such a high-up figure, he cut ties with the anarchists. Now he's searching for a new path in life.
It's clear that the Haunted Doctor is indeed a very intelligent man who will serve a willing zee-captain well. However, despite this, he is a lost soul with little to no sense of self-purpose. The poor man will throw himself at essentially any cause he deems just, even at the expense of his superiors and crew.