Hastur explains that Ashbless is in fact eight hundred years old, initially one of the Knights Hospitaller during the Crusades, but entered a devil's bargain: Ashbless owns Hastur's soul, and is immortal so long as he has it. Should Ashbless give up or lose Hastur's soul (represented by a talisman stylised as an eye—a symbol seen throughout the ship), Hastur would be free to exact revenge upon Ashbless' soul.
Hastur explains that Ashbless is eight hundred years old and was once a Knight Hospitaller during the Crusades, but made a pact with a devil for immortality. The soul of Hastur is represented by an eye-shaped talisman, which if lost or given up will allow Hastur to harm Ashbless.