References to the books can be seen throughout the episodes: the words "electric monk" can be seen on Dirk's office wall before he paints over it and the newspaper headline reads "horse found in bathroom."
The character Richard MacDuff shares his surname with Lord Macduff, the Thane of Fife, a character in William Shakespeare's play "Macbeth".
In the play, Macduff is portrayed as a rational and moral leader, in contrast to the tyrannical, chaos-inducing lead character Macbeth, much as Richard Macduff serves as the sensible foil to the unpredictable Dirk Gently.
In the play, Macduff is portrayed as a rational and moral leader, in contrast to the tyrannical, chaos-inducing lead character Macbeth, much as Richard Macduff serves as the sensible foil to the unpredictable Dirk Gently.