Shepherd Book
Merria Book is a fictional character played by Ron Glass in the science-fiction/Western television series Firefly and its sequel movie, Serenity. He is a Shepherd — a kind of holy man or preacher — and provides frequent spiritual advice and perspectives for the crew of Serenity.
He is almost always referred to as "Shepherd Book", presumably an indicator of his status as a respected religious figure. Book's religion is Christianity (or a future derivative thereof), as he owns a Bible and often references Christian theology.
At the end of the comic "Those Left Behind", Book leaves Serenity. By the time of the beginning of the movie, he had moved to the planet of Haven. In the movie Serenity, Book is killed by a platoon of soldiers sent by an Alliance assassin known only as "The Operative".
Identity
One of the most debated aspects of the show is who Shepherd Book really is. He has some sort of priority status in the Alliance and he demonstrates a depth of knowledge in a number of fields, including ship engineering, firearms, and criminal activities. He often hints at a dark past, but refuses to talk about it. The mysteries surrounding Book's background are never explained in either the short-lived series or the movie.
However, due to his priority status in the Alliance, his knowledge of both martial arts and weaponry and his seemingly intimate familiarity with the Operative's methods, many fans have speculated that Book himself is a former Operative who "lost the belief" and entered the priesthood. In the fourteenth and final episode of Firefly, "Objects in Space", Simon asks Jubal Early, a bounty hunter, why he would beat up Book, a Shepherd. Early replies, "That ain't a Shepherd", implying he has some intrinsic knowledge about Book. A similar insight into Book's past is seen in the same episode when River Tam reads his mind: "I don't give half a hump if you're innocent or not! So where does that put you?" Not only is this an uncharacteristic thought for the religious man, but it is also unclear what he means by this statement. It is likely that if Firefly had continued, Book's past and possible redemption would have been the focus of a story arc. The truth may never be known, as Book perishes as a result of an Alliance attack in Serenity.
This philosophy of this "Holy man with a past" could be a sort of homage to Saint Patrick. Saint Patrick was devout in his ways, yet, in his confession, states that he has committed a grevious sin (some speculate murder) in his past, but refuses to talk about it, instead focusing on the spread of his beliefs, much like Merria in Firefly. Furthermore, the "Holy man with a past" character is not unknown in westerns (or even space westerns, see: Trigun).