Mike is a cynical author who makes his living writing the popular "Ten Nights" series of haunted travelogues. Originally an aspiring poet and literary writer, he abandoned his artistic ideals for commercial success. He approaches his paranormal investigations with extreme skepticism, believing his readers are gullible, yet he subconsciously maintains personal superstitions, such as wearing an unlit cigarette behind his ear.

Olin is the meticulous and polished manager of the prestigious Hotel Dolphin in New York. Carefully manicured and dressed in a perfectly knotted tie, he embodies the upscale aesthetic of the establishment. He possesses an encyclopedic knowledge of the hotel's history and takes his responsibilities highly seriously, acting as a protective barrier between the public and the dangers of room 1408.

Sam is Mike Enslin's pragmatic literary agent. He operates entirely in the commercial publishing world, far removed from the eerie environments his client investigates. He focuses heavily on the profitability of Mike's "Ten Nights" series and eagerly anticipates the financial returns of a new installment.

Rufus is a sewing machine salesman and a guest staying on the 14th floor of the Hotel Dolphin. His presence introduces a mundane, everyday element to the otherwise ominous environment of the hotel's upper levels.

Donald is Mike's older brother who passed away from lung cancer. His memory frequently surfaces in Mike's thoughts, heavily influencing Mike's anxieties surrounding death and his habitual attachment to an unlit cigarette.

Robertson is the lawyer who represents Mike Enslin. He utilizes legal loopholes and pressure tactics to force the Hotel Dolphin to accommodate Mike's demand to stay in their notoriously closed-off room.

Jane Smiley is an American novelist who taught Mike Enslin during his college years. She encouraged his early attempts at serious literary fiction before he pivoted to commercial ghost travelogues.

The head housekeeper is a long-standing employee at the Hotel Dolphin. Originally working alongside her twin sister, she is the only staff member Olin trusts to conduct the monthly cleaning service in the dangerous room.