Bento isn't really a character per se, since he's dead before all the events described take place. That said, he's definitely a presence… but, don't worry, not in the creepy haunted house way. A crazypants former dictator of Costaguana, he was responsible for imprisoning and torturing a lot of his countrymen, including some of our characters (e.g., Doctor Monygham and Don José). He also killed Charles Gould's Uncle Henry.
While he was in full swing fighting a conspiracy that, from all reports, was entirely imaginary, he died of an apoplectic fit… basically an old-timey word for a stroke.