After crossing the sea guided by the Bellman's map of the Oceanâa blank sheet of paperâthe hunting party arrive in a strange land, and the Bellman informs them of the five signs of a Snark: its "meagre and hollow, but crisp" taste; a habit of rising late and taking breakfast during five o'clock tea; "its slowness in taking a jest"; a "fondness for bathing-machines"; and its ambition. The Bellman warns them that some Snarks are highly dangerous Boojums, causing the Baker to faint. Once revived, the Baker recalls that his uncle warned him that if the Snark turns out to be a Boojum, the hunter will "softly and suddenly vanish away, and never be met with again." The Baker confesses that the notion of this sudden vanishment brings him much distress.
With this in mind, they split up to hunt the Snark: "They sought it with thimbles, they sought it with care; / They pursued it with forks and hope; / They threatened its life with a railway-share; / They charmed it with smiles and soap." Along the way, the Butcher and Beaver, previously mutually wary, become fast friends, after the Butcher teaches it more in ten minutes than it could learn from books in seventy years. The Barrister, meanwhile, dreams of the court trial of a pig accused of deserting its sty, whom the Snark is defending. The Snark, however, finds the pig guilty and sentences it to transportation and a fine of forty pound. His dream concludes with the jailer informing the court that the pig has actually been dead for years, to the judge's disgust.
During the hunt, the Banker finds himself attacked by a bandersnatch, and loses his sanity after trying to bribe the creature. At the conclusion of the poem, the Baker calls out that he has found a snark, but when the others arrive, he has mysteriously disappeared, leading the narrator to explain: "For the Snark was a Boojum, you see."

Question: Which character loses his sanity?
Answer: Banker
Alternative answer: the Banker