The Antagonists are the main villains of each season. While all seasons have a main antagonist, some may have a secondary antagonist, and more than one of both. Also, while most are usually serial killers, there are a few examples of antagonists who are not considered serial killers. Although a killer appears in nearly every episode of the series, only ones who have posed a serious threat to Dexter or another main character for more than one episode are listed below.
Brian Moser, under the name of Rudy Cooper, is the first season's Main antagonist. Dubbed the "Ice Truck Killer" by Miami Metro PD, Brian is actually Dexter's older brother and uses his victims in an elaborate scheme to help Dexter remember his past and reunite them as a family. Dexter eventually uncovers his origins, but rejects Brian in favor of the life he has managed to live using the Code of Harry. Knowing Brian will never stop trying to "free" him from his normal life, Dexter kills him, making it look like a suicide.
The secondary antagonists for this season include Carlos Guerrero and Sergeant James Doakes, who only starts to really suspect Dexter near the end of the season. Detective McNamara can also be considered an antagonist in Doakes' plot, though a temporary minor one. The reason behind Mac being an antagonist is strictly the bare basis of the term...he opposes Doakes, views him as his enemy and does what he can to get back at him. Paul Bennett is also an antagonist in Rita's plot
Lila, whom Dexter meets while attending a narcotics anonymous meeting (an act he is putting on as part of a lie to Rita) is a sociopath with a propensity to burn things. She and Dexter form a complicated relationship as Dexter believes she can help him resist his Dark Passenger, while Lila believes Dexter is her soul mate and is willing to harm anyone who she sees an obstacle to them being together. Dexter eventually realizes her dark obsession with him and breaks things off, which leads to Lila stalking him and the other people in his life.
Sgt. Doakes, who always found Dexter strange, is now convinced that Dexter is up to no good and actively stalks him, which prevents Dexter from satisfying his homicidal urges. Dexter is able to shake him for a while, but Doakes eventually catches Dexter red-handed by placing a GPS tracker on his boat, the Slice of Life. Dexter manages to overpower Doakes and holds him captive for several days inside a remote cabin in the Everglades. Even though it would make life easier for him, Dexter refuses to kill Doakes because he does not fit the code. During his captivity, Doakes and Dexter have several conversations that show the two understand each other more than either was willing to admit before. Dexter, knowing he can't kill Doakes, begins to plant evidence to frame him for Dexter's own crimes, but eventually resigns to the idea that he must turn himself in. The last time Dexter and Doakes speak, Dexter tells him he really enjoyed being able to speak openly and honestly with him.
Lila and Doakes meet for the first and only time when a distraught Lila steals Dexter's GPS and uses it to find the cabin, where she finds Doakes still in captivity. Doakes reveals that Dexter is a serial killer, but rather than set him free, Lila decides instead to kill Doakes. She does so to remove another threat to her relationship with Dexter and because she believes being a killer like him will bring them closer together. She blows up the cabin, killing Doakes and inadvertently completing Dexter's frame job on him before Dexter is able to turn himself in.
When Dexter rejects her again, Lila tries to kill him along with Astor and Cody before fleeing the country. Dexter eventually tracks her down in Paris where he quickly kills her, using drugs on her to keep her from feeling the pain.
Only one major secondary antagonist for this season, being Santos Jimenez, one of the men who aided in the death of Laura Moser and attempted to kill Dexter after being confronted and attacked by him. He is later killed by Dexter in the same way Santos killed his mother.
Both men become part of Dexter's life as result of Dexter's victim Freebo. When Dexter first attempts to kill Freebo, he is attacked by Oscar Prado, whom he kills in self defense. Dexter is able to frame Freebo for the crime, but after hunting down and kill Freebo himself, he is caught by Miguel, who, rather than turn Dexter in, thanks him and the two becomes friends.
An uneasy trust builds between the two men, and with Dexter eventually opening up about his other vigilante murders after Miguel makes it clear he supports such a thing and shows an interest in participating himself. Though Dexter resists at first, he eventually teaches Miguel some of his methods and code. After Miguel commits his first murder with Dexter, though, he has bloodlust and murders a defense attorney he dislikes. When Dexter chastises him for this, their friendship falls apart and the two struggle to gain leverage over the other.
Meanwhile, King, a former Nicaraguan solider working as a tree-trimmer, begins searching for Freebo, who owes him a large sum of money. When he is unable to find Freebo, he begins torturing and killing those with ties to him. He is dubbed "The Skinner" after his chosen method of torture.
Dexter ultimately decides he must kill Miguel to stop him and he does so by straggling him and framing the death on King. Though Dexter is not heavily involved with the Skinner case, he knows enough to copy the MO of King. However, before he is killed, Miguel, in an effort to have Dexter taken out, tells King that Dexter is the only person who knows the location of Freebo. King kidnaps Dexter and prepares to torture him but Dexter manages to break free and kill him.
The main secondary antagonist for this Season would be Ramon Prado, brother to Miguel. After his brother's death, Ramon becomes obsessed with finding Freebo no matter what the cost. He starts antagonizing Miami Metro Homicide as not doing their job but mainly antagonizes Dexter for his close relationship with his brother. After he is found torturing a suspect for information on Freebo he is forced out of the Sheriff's Department on early retirement. He eventually comes after Dexter when his other brother Miguel dies and tries to kill Dexter only to fail and taken into custody. He is later seen realizing that all his anger is towards Miguel and now that he is dead, he is free and is let go as one more favor to the Prado family and isn't seen since.
Freebo may also be considered one of the main secondary antagonists, since he was instrumental in the main antagonists being involved in the storyline.
Arthur Mitchell, also known as the Trinity Killer, is the main antagonist of season four. After discovering that Mitchell has a family and has successfully lived a dual life for more than thirty years as an active serial killer, Dexter tries to befriend him in an effort to learn how he does it. Though he knows the risk Mitchell poses, Dexter lets him live on several occasions, even going as far as to stopping Mitchell from committing suicide, because he thinks he can learn from him. Eventually, Dexter discovers Mitchell's "happy" home life is a sham, and his family are really just terrified of the mentally and emotionally unstable Mitchell. Mitchell, however, figures out Dexter's deception, and while he thinks Dexter is only trying to extort him, he threatens to destroy Dexter's life if he doesn't leave him alone. Dexter eventually manages to trap and kill Mitchell, but not before Mitchell made good on his promise to destroy Dexter's life. After disposing of Mitchell's remains, Dexter comes home to find his wife, Rita, dead as Mitchell's final victim.
Christine Hill, Arthur's daughter, is the main secondary antagonist who is a reporter that begins dating Joey Quinn to keep tabs on the police and find out how close they are to catching her father. Christine has major daddy issues, willing to do anything to make Arthur love her, but is unfortunately shut out by him at every chance. When Frank Lundy gets close to figuring out Trinity's identity, Christine kills Lundy and injures Debra Morgan, making it look like a "Vacation Murderers" crime. After Christine lets a detail of the crime slip while talking to Deb, Miami Metro finds out she killed Lundy and that she's Trinity's daughter. Ultimately, she commits suicide after Arthur abandons her and Debra refuses to forgive her.
Johnny Rose and Nikki Wald are also secondary antagonists being a sub-plot for LaGuerta and Batista on how they run the investigation. After they kill two people LaGuerta and Batista go to Nikki's house where they open fire on them and escape. They are later blamed for the shooting Christine did and Batista runs a story revealing Johnny's status as a carrier of syphillis which Nikki reads. After an argument she ends up killing Johnny and she is taken into custody. She confesses to every crime she committed but not the Lundy shooting and after awhile people are able to realize they were not responsible.
Jordan Chase, Stan Liddy and Joey Quinn are the main antagonists for this season. Interestingly enough, Jordan Chase is the only serial killer main antagonist that Dexter does not kill. He does, however, kill Stan Liddy.
The barrel girl gang, a raping/killing circle folds out as the main target of Dexter in season five. The circle is responsible for raping and killing several women, including Lumen Pierce, their thirteenth known victim, and one of only two to not be killed. All five men appear in a photo, taken by their first apparent rape victim Emily Birch. Famous author and motivational speaker Jordan Chase is revealed to be the driving force behind the circle. As members of the circle begin to Disappear, Debra deducts that their latest victim escaped and is exacting her vengeance, with the possible help of the man who loves her. While Debra eventually arrives at the camp, almost catching the vigilante couple (in reality, Dexter and Lumen, hidden behind an opaque plastic and therefore, unseen to her), she spares them by advising them to disappear before the police arrive.
In this season the main antagonist is Travis Marshall, The Doomsday Killer. Professor Gellar was thought to be working with Travis, but he was found dead, presumably killed before the season started. Travis is the first antagonist to have a Dark Passenger appear in physical form, and the second character overall (Dexter Morgan being the first). His Dark Passenger manifests itself as Professor Gellar.
Traiv's dark passnger, which temporarily takes the form of Professor James Gellar, is considered the most primairy secondary antagonist of the season.. Until he is revealed to be Travis' Dark Passenger, Professor Gellar, was believed to be one of two Doomsday Killers, thee other being Travis himself. In this scenario, Gellar was seen as Travis' mentor figure and the leader of the serial killer patnership, making him a candidate for being the Main Antagonist. Even as a passenger, Gellar is considered a secondary antagonist as he is part of Travis, at least until Travis makes the realization that Gellar had been killed long ago. As Travis' dark side to his split personality, Gellar personofies the evil in him for three fourths of the season, so he is considered to be a significant, if not the most significant antagonist of that portion of the sixth season.
Brian Moser appears in the episodes "Just Let Go" and "Nebraska". After "avenging" Brother Sam's death, Dexter convinces himself there is no light in him, only darkness in the very end of "Just Let Go". Brian appears behind him and gives him a round of applause. In the episode "Nebraska" Brian tries to tempt Dexter into giving up the code and to just be a killer. Dexter eventually fights Brian off and re-accepts Harry and his Code.
Steve and Beth Dorsey are also secondary antagonists, being recruited by Travis Marshall after he realizes Professor Gellar is dead. They assist in the murder of Holly Benson, and help in creating a Doomsday Tableau, Wormwood.
Louis Greene also appears starts to become a secondary antagonist at the end of the season where it is revealed he bought the hand from Ryan Chambers and later ships it over to Dexter's house to mess with him.
The street gang, the Locos are also secondary antagonists. They were in conflict with Brother Sam when Sam was trying to reform Nick, a former member. Dexter killed the gang's leader, Julio Benes, and the gang's lieutenant, Leo Hernandez, was killed by Miami Metro. After it was revealed that Nick killed Sam, Dexter killed Nick.
The Koshka Brotherhood, a Ukrainian/Russian Organized-crime syndicate, folds out as the main target of Dexter in season seven. The Brotherhood is responsible for the deaths of numerous people including but not limited to Kaja Soroka, Mike Anderson, Tony Rush, Alex Dubrozny, Andres Rodriguez, two unnamed Columbians.
Isaak is the Don of the Koshka Brotherhood who comes to Miami after his lover Viktor Baskov never makes his flight to Kiev. He leaves a trail of bodies in search for Viktor which Dexter begins to notice after he finds blood on his boat. Dexter then tries to have Isaak killed through their Columbian rivals but underestimates Isaak's skills as he kills all the assassins with ease. He is arrested for the murders but is let out due to some evidence tampering by Joey Quinn at the behest of George Novikov. He tries to kill Dexter again in the donut shop from a distance but fails. Dexter tries to kill him but unintentionally save Isaak's life when he kills a hitman sent to kill him. He and Dexter form a complicated relationship as Dexter begins to realize why Isaak wants to kill, while Isaak, still wanting to kill him, believes Dexter could have been friends under different circumstances. Isaak eventually forces Dexter to help him kill some more assassins sent to kill him with Jurg holding Hannah hostage. Isaak also promises to leave Dexter alone after it's done and they begin working together. Dexter kills the first assassin with ease and leads the other one into a trap for Isaak to kill him. Just when Isaak thinks it is done George appears and shots Isaak himself. As a last request Dexter takes him to the spot where Dexter dumped Viktor and gives Dexter one last piece of advise about love before he dies.
Captain LaGuerta, who always believed Doakes was never the Bay Harbor Butcher, is now convinced that Butcher is alive and killing more people when she finds a blood slide at Travis Marshall's crime scene. Debra is able make sure that there is no evidence linking Dexter to any of the murders and for awhile it seems she gave up. Maria then begins to suspect that Dexter is the Bay Harbor Butcher when she sees his name on a list of boat owners. She eventually goes to Matthews to help in this where he initially refuses but decides to do it and in exchange Maria will give Matthews his full pension. She tries to get him on board with the possibility that Dexter is the Bay Harbor Butcher but he thinks she's nuts. They go to the Everglades cabin where Doakes died and discover that it was being rented by Santos Jimenez, one of the men that killed Dexter's mother and Maria uses this to try and talk to Dexter but Matthews refuses and says he'll talk to him because she blast him with this. In the meantime she recommends to the parole board that Hector Estrada, the man who ordered Dexter's mother's death, to be released in order to bait Dexter. LaGuerta and Matthews then find a warehouse with "evidence" proving that Doakes was the Bay Harbor Butcher but Maria is not convinced and prepares for the takedown. She has two detectives backing her up and preparing to arrest Dexter for Estrada's murder but arrives too late as Dexter has found out about what she did and he and Estrada are long gone. To get her off his chest Dexter anonymously sends her false evidence that shows him killing Hector Estrada and has him arrested. When she finds out the evidence is fake she is beyond herself but eventually calms down when she receives a video from Mike's widow showing Debra getting gas from a local station right near the church where Travis died. When she confronts Debra she denies setting the church on fire and she leaves while Maria prepares warrants to get the GPS on Deb and Dexter's phones showing they were there the night of Travis' death. Dexter find this out and sets a trap for Maria using Estrada who she thought was dead and injects her with some M99 in order to frame her for killing Estrada and vice-versa. When Deb appears and wakes up she tries to convince Deb to shoot him but ends up shooting Maria herself. Deb immediately horrified at what she did grabs her body in tears.
Viktor Baskov, George Novikov, Jurg Yeliashkevych, Oleg Mickic, and Benjamin Caffrey are all secondary antagonists this season, since all of them are part of the Koshka Brotherhood. Viktor Baskov, who kills Mike Anderson, is the first member of the Brotherhood to appear in the season, and is killed by Dexter. His death can be seen as an incentive for much of the season's conflict as it was to avenge him why Isaak arrives in America in the first place. Novikov also had a sub-plot as an antagonist to Joey Quinn, using Quinn's girlfriend Nadia, who was owned by the Koshka Brotherhood, as leverage to force Quinn to assist in the Brotherhood's operations.
Hannah McKay is also a secondary antagonist for a completely different reason.
Louis Greene is also a secondary antagonist, as his inner nature becomes more apparent this season. He breaks into Dexter's apartment and steals his credit card numbers and cancels them. After Dexter returns the favor by breaking into his home investigating why Louis sent him the hand he finds a collection of evidence showing Louis' true nature. Dexter finds his credit card numbers, a video of Louis cheating on Jamie Batista with a hooker and evidence that suggests he planted child pornography on his partner Robert Henley's computer, having him arrested by the FBI. When confronted he confesses that it was because Dexter "shited" all over Homicidal Tendencies and he was trying to screw with him. Dexter told him to get out of his life but Louis wouldn't back down. Dexter thought about killing him and even came close until he backed out because of Debra's advise. Dexter decided to send evidence of Louis' offenses to two people he had close relationships with: Vince Masuka and Jamie Batista. He sent Vince the hand to get Louis fired from his job and sent the video of a hooker giving him a blow-job to Jamie causing her to dump him. Louis tries to sink Dexter's boat in revenge for this but is caught in the middle of this by the Koshka Brotherhood where he is killed by them.
Ray Speltzer is also a secondary antagonist who kidnaps women and tortures them by chasing them through elaborate labyrinths, wearing a bullhorn helmet. Once he has caught up to them, he brutally beats them to death and takes their earrings as trophies. He attempts to kill Debra Morgan and also traps Dexter in his most elaborate labyrinth, only for him to escape. Dexter later kills Speltzer, putting his body in a crematorium.
Sal Price is also a secondary antagonist. An investigative journalist and true crime author, Price came to Miami to cover the Hannah McKay case, and was also a brief love interest for Debra Morgan, who he assisted in the investigation of McKay. When Price discovered the relationship between Dexter and Hannah, he used it to blackmail Dexter into giving him info about Wayne Randall's last moments. In order to keep Price from publishing information about Hannah, Dexter deleted all of Price's files and threatened to release evidence that would implicate Price in a previous murder he had been reporting on. However, Price is poisoned by Hannah before Dexter can put his plan into effect, and dies in Dexter's apartment.
Joe Jensen is also a secondary antagonist. Known as the "Phantom Arsonist", he is coerced by his dark passenger "Bobby" to burn people alive. He was nearly killed by Dexter, but Dexter allows him to live at the last minute and then left him for the police to find.