He is a Shepherd (the literal English translation of the clerical title "Pastor", from the Latin), and provides frequent spiritual advice and perspectives for the crew of Serenity.
[1] However, by the time the film was completed, Joss Whedon changed his first name to Derrial, which is the way it appears in all printed official works based on Firefly.
"[3] Glass stated that Whedon and the costume designer Shawna Trpcic "had a pretty clear idea of how they wanted him to look", and how he appears in the pilot with a distinctly priestly collar and scant possessions "was a strong reflection of the character".
[3][4] Glass, himself a Buddhist, found it intriguing to play this role: "What I was able to bring to the Christian part of it was the humanism and the humanistic point of view.
He holds some sort of high priority status within the Alliance, and on numerous occasions has demonstrated a depth of knowledge in a number of fields one would not expect a clergyman to be familiar with, including space travel, firearms, hand-to-hand combat, and criminal activity.
"[3] In the 14th episode of Firefly, "Objects in Space", Simon berates the bounty hunter Jubal Early for assaulting Book, a Shepherd.
"[6] In the DVD commentary Firefly, Whedon states this is due to Early's intuition and ability to quickly size people up.
Though the exact information on the card is never shown, the crew does note that it affords Book urgent and immediate access to the medical facilities on board, as well as free passage for Serenity without the expected inspection.
[8] Several other episodes contain allusions to Book's past; in "The Train Job", he is aware of the identity of crime lord Adelei Niska,[9] while in "War Stories", he displays a working knowledge of high-powered weaponry, first to identify sharp-shooters and later to take part in a coordinated assault against Adelei Niska's space station.
[10] On the 2007 Browncoat Cruise, Ron Glass revealed with Whedon's permission several facts about Book, including that Derrial was not the shepherd's real name, but the name of a man he had killed.
The original script for pilot episode "Serenity" includes this scene establishment: "We see, passing through frame, Shepherd BOOK.
At one point while critically injured his identification card earned him immediate treatment from Alliance medical personnel when their commanding officer had originally left him to die.
The shock of Book's death, and the realization that he can't hide without endangering everyone he meets, leads Mal to stop running.
He ran away from home and began life as a petty criminal before being recruited by the Independence movement and moving out to the Border Worlds.
Media scholar Michael W. Marek described Shepherd Book's character as "the preacher with a secret past", which is "a common Old West archetype", although Firefly is set in the future.
[4] Arts commentator Eric Greene described Book as "an endless font of paradox that drew me in, made me want to know more" and wished the character had not been killed in the Serenity movie, feeling that "something worthy was lost" from the franchise.
Greene felt Book stood for many benign, compassionate types of believers, and that the removal of the character denied them "a place in the Whedonverse".