Dexter: "The only way to kill a Dark Passenger is to take out the Driver."
"The Dark Passenger" was a concept used within the DEXTER Universe that represented the "demon" inside of all of the Murderers that actively made them do terrible things. While it was actually being built upon as an entity in the novels, it was more or less (in the tv series) the level of "darkness" and instability in each person's personality that could either control them or be contained.
Originally, the "Dark Passenger" was Dexter's way of naming the "desire to kill" that entered his spirit, after witnessing his mother's brutal death. This "Dark Passenger" was always trying to 'claim' him, wanting him to kill, but he was able to keep it at bay with a high level of control, and, instead of focusing his urges on innocent people, he only used them on those who were guilty.
As of Season Seven, Dexter began viewing his "Dark Passenger" as a scapegoat for what he was responsible for during all of the previous years. At this point, it appeared that he viewed all of his actions to be his own, rather than an urge created from a dark personification. Regardless of this fact, the "Dark Passenger" can be metaphorical and can represent why someone is driven to kill, and what made them the way they are.
During The Finale, Dexter managed to completely abandon the idea of this "demon" inside of him (after his sister perishes at the hands of "himself"; In reality, a blood clot created from her gunshot injury ultimately placed in her in a vegetative state, which forced Dexter to shut off her life-support), which shows that Dexter is not the easily controlled and subjugated person that was rumored by Dr. Evelyn Vogel. The abandonment of his "passenger" allowed Dexter to move on with a livelihood (being a lumberjack) that he most likely hoped would utilize the rest of his life. However, Dexter lost quite a lot of his humanity after losing his sister and others close to him.
There are a total of ten major passengers within the series, each driving a character's dark urges into reality. There also may have been a eleventh and/or twelfth passenger, not listed below, belonging to Jordan Chase and Isaak Sirko, respectively.
Jordan Chase was the main antagonist of Season Five, and there were implications throughout the series that he had a Dark Passenger, though the cause of it is unknown. For starters, he seemed to take a strange liking to Dexter, much like the way Lila, Miguel and Arthur did...this is likely because he, like all of them, recognized Dexter as someone like himself in a way, albeit without knowing it. He was also capable of pretending to be a nice, likable person while at the same time being a sadistic serial killer responsible for the vicious murders of people he didn't even know. He has even proven himself to be every bit as dangerous as Dexter was when he successfully fooled and bested him on a few occasions throughout the series, as well as seeming to have an unusually high understanding of him... just like his fellow main antagonists. All of this implies that he had his own Dark Passenger, though the cause of it is never revealed.
Isaak Sirko was one of the main antagonists of Season Seven, who, like Jordan Chase, is implied, but never confirmed to have a Dark Passenger. He identified Dexter as someone similar to himself, and even remarked that in another world, the two could have been great friends. He also is extremely interested in Dexter's motivation for killing, being to avenge the victims of the people he killed. This is similar to Isaak's own reason for wanting to kill Dexter, which is for killing Isaak's secret lover, Viktor Baskov. Although Isaak had a history of being violent, dating back to the act of pushing his music teacher down a flight of stairs, it is implied that Isaak's passenger, if he had one, developed during Isaak's time at an English boarding school, as Isaak states that afterwards, he didn't have much left of a sensitive side left. Although Isaak's impulse to kill Dexter is hard to control at first, as he is tenacious about getting his vengeance on him, despite ending up being arrested and hindering the operations of the Koshka Brotherhood, Isaak eventually spares Dexter, although it is because he needed his help in killing Oleg Mickic and Benjamin Caffrey, two hitmen out to kill Isaak.
Dexter Morgan's "Dark Passenger"
This passenger is one that has not won over Dexter, instead it constantly sits in the dark fueling Dexter's urge to kill. Whenever Dexter becomes unable to kill, it becomes irritable and near drives him mad because of it. Whenever Dexter hits a strong emotional situation, it springs out to take advantage of the moment and on one occasion forced him to kill a man he knew nothing about.
So far, Dexter is in control of his passenger, so much so that he knows who to kill and to channel it away from the innocent.
Dexter is driven to kill to satisfy an inner voice he calls Dark Passenger. When that voice cannot be ignored, he "lets the Dark Passenger do the driving". In the books, it is assumed that this is Dexter's way of referring to his homicidal urges but it was revealed in the third book that it might in fact be a real demon deep inside Dexter. The idea was largely disliked by critics and fans alike and was dropped from future books. It is mentioned in the TV series but only as Dexter's way of referring to his urges and with significantly less frequency than the books.
Dexter is one of only two characters to have the Dark Passenger appear to them as a physical form (the other being Travis Marshall with Professor Gellar). So far, his passenger has manifested itself in three forms - Brian Moser, Harry Morgan, and Laura Moser. A third Passenger, belonging to Joe Jensen, which although is not known to take on a physical form in the killer's mind, does take the name of Jensen's childhood friend, Bobby.
Dexter comes to the conclusion in Episode 10, Season 7 that the dark passenger does not exist as a separate entity, and was a way of evading responsibility for his actions. His father, Harry, and Trinity thought that Dexter's passenger would stay inside him forever, however, Dexter at one point, thought that it might eventually leave him. It is unknown if the dark passenger is still inside him currently, however, one of the writers implied that his passenger is still inside him.
Brian Moser's "Dark Passenger"
Brian's passenger was born during his mother's terrible death at the hands of Santos Jimenez and two other men, Lipsey and Welsh. His brother Dexter Morgan was also there and formed his own passenger.
This passenger is on the dominant side of control within Brian, as opposed to Dexter, feeding off his perverse fascination with limbs and fueling his desire to kill innocent women that are typically prostitutes. His passenger is not a spur of the moment kind of creature however and will not enable him to kill his own brother, instead wanting to separate his brother from a woman whom he views as being a problem - Debra Morgan.
Brian takes immense pride in what he does - thus, his passenger is kept happy by displaying his trophies in public to lure in his brother.
Lila West's "Dark Passenger"
Lila's passenger was born in the past and is attracted to fire above all other things. Because she only experimented with it one time before, the sudden use of it again fascinates her.
This passenger feeds off of her negative emotions towards something, acting out when she's most vulnerable to its control. Her demon can, and will make her spontaneously burn anything in sight (even her prized possessions and works of art, that could have earn her thousands of dollars). Killing people has no effect on her, and it is uncertain that her Dark Passenger actually desires to kill, rather than to simply burn everything in sight. Thus, while she and her passenger may certainly be destructive, Lila appears to lack the murderous drive of a true killer. When she meets a man (Dexter) who does, however, and realizes that he too has a Dark Passenger, she believes that she has met her soulmate; somebody like her in a way at last.
Lila becomes fascinated with the flames she watches, feeling almost at ease when watching her arsonous works run their course. It proves that Lila's dark passenger was overtaking her.
It is unknown exactly what the cause of her passenger was, but she once told Dexter that she had killed her boyfriend in a house fire after, in addition to frequently being beaten up by him, finding out that he was a drug dealer. Assuming this story was true, it is possible that it may have been the emotional scarring caused by his deceit and his murder that created her sociopathy and passenger-just like Dexter and Brian were recreating the death of their mother and Arthur was recreating the death of his family, Lila may have been recreating the fiery death of her deceptive boyfriend when she sets things on fire. It is possible that she did not actually see him burn alive, just saw the house burn down-that may explain why she is only interested in burning objects and not really people. As a result of her sociopathic tendencies, however-most likely caused by his abuse-the concept of killing innocent people if she has to in order to get what she wants is not one that she has a problem with, which is why Dexter does not believe that they are soulmates.
Miguel Prado's "Dark Passenger"
The date of creation of Miguel's passenger is difficult to place, as it could have been born at any time during his life (possibly early on, due to his father visiting physical abuse upon his children; or, perhaps later on as he built up rage towards those criminals who escaped what he believed to be an inefficient judicial system).
This passenger is greedy - so greedy, that it will dispose of whatever and whoever stands between Miguel and his ambitions. However, Miguel is reluctant to kill his friend Dexter after their friendship falls apart, showing that he has some semblance of control over his inner evil.
Miguel has a fascination with his killing and sees it as a tool to achieve what he wants, culminating in his possession of a cheerful demeanor within hours of having committed murder. He was also willing to kill LaGuerta in order to cover his tracks when he realized she knew he had killed Ellen Wolf, another example of his perception of murder as being necessary in certain situations. His passenger likely stems from his hatred towards criminals like his abusive father and anyone responsible for a miscarriage of justice that gets them off-as a result he channels his passenger only towards those who, in his opinion, deserve to die, just like Dexter. However, because his passenger is caused by a hatred of people who get murderers off the hook as well as murderers themselves, he basically perceives anyone responsible for a miscarriage of justice as someone who deserves to die, which is what led to his murder of defense lawyer Ellen Wolf, a woman who was innocent by Dexter's standards.
George King's "Dark Passenger"
King's passenger was born in his violent past, slowly coming to light as he killed in the past. His background of torturing and skinning people for a living caused him to become a control freak who valued respect-when he believed Freebo had disrespected him, it caused him to develop homicidal urges aimed at him and anyone who was associated with him.
The thing about King's passenger is that he never really accepted he was a serial killer, though it was feared by many around him. He certainly didn't like being called pathetic for having little to no control of what he did because he used an excuse to mask his murderous intent. King always used something (such as Freebo) to justify his kills in search for his money, and despite being confronted that this was a sham and he truly didn't care about the money, his mind quickly sets into place that he wants Freebo again, thus having no acceptance of what he really is. Whether he cared to admit it or not, however, the thing he really wanted was for Freebo to show him the thing he valued so much that his passenger was created just because he believed that Freebo had refused to show him any-respect.
King takes pride in leaving his victims out but not as a way to be caught, most likely to get Freebo's attention or something of that matter.
Arthur Mitchell's "Dark Passenger"
Arthur's passenger was born after his sister's death, topped off by his mother's suicide and his father's abuse and later murder-which was likely committed by Arthur himself.
Arthur's "demon" is very violent and is practically in complete control of his life. Dexter fears that the same will happen to him if he lets himself lose to his passenger, but Arthur is a perfect example of what might happen in Dexter's future if he isn't careful. Arthur admits that he has no control over his demon and instead wants to be stopped, even going so far as to try and kill himself to stop these constant murders. He never takes pride in his killings.
Despite Arthur's dark passenger, he regrets all of his murders, but is unable to stop himself willingly and would rather have someone else stop him. It takes a lot to make him realize this and he finally accepts his fate, having his dark passenger die along with him.
Lumen Pierce's "Dark Passenger"
Lumen's passenger was born during her torture and rape by The Group and is an actively developing feature about her.
Lumen's passenger is random and unplanned, however, it gives her an acute ability to find people out, sense danger and other techniques she wouldn't normally have. So far, it has wanted her to kill the men responsible but because of Lumen's inexperience with these things, she can't do much with these claims. However, she always wants to make a point (violently) and hurt those that hurt her.
She doesn't take pride in her passenger, and, much like Dexter, she wishes to channel it only towards the guilty-towards men who deserve to die in her opinion, and by Dexter's standards deserve to die also. For example, she is disturbed by Dexter's calm personality and skill throughout the killing of Cole Harmon-she was uncomfortable, almost horrified, as it became clear to her that Dexter had done this many times before. Her conflict about what she is, and desire to punish only men who have murdered, makes her more like Dexter than Miguel could ever be. Her dark passenger disappears when The Group finally dies.
Travis Marshall's "Dark Passenger"
Travis Marshall is the main antagonist of Season 6. His dark passenger is the most unique of all the antagonists encountered by Dexter. Similar to Dexter, his dark passenger talks to him in the physical form of his deceased mentor, Professor Gellar. Since Travis suffered from dual personality disorder, his dark passenger appeared only to his good side and it appears to treat Travis like its son, only wanting him for itself and not letting anyone else come in its way, leading the dark side of Travis to kill Lisa Marshall, his own sister. Although in the end after Travis comes to the realization that Gellar has been dead all along and he was himself responsible for all the murders, he accepts the darkness inside him and abandons the dark passenger (as he no longer needs its help).
Travis Marshall's Dark Passenger talks to him just like Dexter's does...while Dexter's passenger talks to him in the form of his father and his brother (both of whom are deceased) Travis' talks to him in the form of his mentor, again, who is dead. Not only that-it has mutated into multiple personality disorder, as Travis is now switching from one personality-his own-to the other-his Dark Passenger's in the form of Professor Gellar when it takes over. The cause of it, however, is unknown.
Hannah McKay's "Dark Passenger"
Hannah's dark passenger was created from the part where she nearly died from drowning by her father throwing her in the water when she was six.
Daniel Vogel's "Dark Passenger"
His passenger was born upon being neglected by 'his mother', who focused of all her attention towards her younger son (Daniel's brother). As a response, Daniel drowned his younger brother in a swimming pool and he was, in turn, sent away to a mental asylum. While there, he was practically tortured - Having to be tied down to a chair and force-fed his medications. Saxon had had enough this, and so deliberately caused an immense fire that would allow him to escape, while killing a sufficient number of children in the process. He was able to frame a by-standing nurse for the incident. After the incident, he used his freedom to journey around the world, during which he spent time killing people. He later decided to move to the United States, firstly Texas and then Florida (Tallahassee and Miami). In Miami, he began murdering people, carving into their craniums, and then harvesting their brain fragments (particularly, the anterior insular cortex). He spent much of his time here (at least, after The Brain Surgeon Investigation began) concealing himself, even going to the trouble of using patsies and framing a man with a cicatrix on the back of his head; All of this was a way to test Dexter Morgan and his own mother, who was residing in Miami as well. After a long search for the Brain Surgeon, Dexter eventually discovers that it is none other than Vogel's "long lost" son, and the two secretly meet up one day. While the two seem to act pleasant towards one another at first, this is cut short when Daniel cuts her throat in front of Dexter. Vogel is later avenged when Dexter stabs Oliver in the neck, killing the latter.
The Dark Passenger is revealed in the third novel, Dexter in the Dark, to be an independent agent inhabiting Dexter, instead of a deviant psychological construction.
It is revealed that the Dark Passenger is the offspring of Moloch, a god who has been worshiped since Biblical times. When Dexter was 3, he and his brother were left in a tanker full of blood and dead bodies, and as a result Dexter became emotionally numb. The pain also drew the Dark Passenger to him, which may be the true reason for his desire to kill as opposed to any psychological deviance.
After Dexter in the Dark, it seems that the idea of the dark passenger being a living entity has been abandoned. As of 2013, writer Jeff Lindsay stated In The Dark was an experiment, and as such the storyline was been tested, assuming the reviews regarding the novel, Lindsay dropped the idea.
During the beginning of the novel, Dexter is still feeling the somewhat weak and backseat-like attitude of his Dark Passenger, caused by the events of Dexter in the Dark.
In the first season, the Dark Passenger is mentioned as a general term for the burden Dexter carries as a result of his trauma.
In the second season, it is used to refer to an impulse like drug addicts have.
In the sixth season, Dexter's Dark Passenger started to manifest in his consciousness as his dead brother Brian Moser, commenting and influencing his attitudes, similar to the way he interacts with his father's presence in his mind. This shows the light and dark side of the passenger, contrasting that of the James Gellar passenger in Travis Marshall.
In the seventh season, Dexter, with the insight of Hannah McKay, who had no passenger of her own, begins to start viewing his passenger as an excuse for killing that he himself adopted. This revelation is finalized with a confrontation with Joe Jensen, the 'Phantom Killer', who had his own 'passenger' that coerced him into burning people alive. Since this idea, the majority of Dexter's kills weren't ritual kills for avenging victims, but were more for the purpose of defending himself or others, such as Hannah. These kills included Oleg Mickic, Clint McKay, and Hector Estrada.