Captain María Esperanza del Alma LaGüerta was a main character on DEXTER. She was the Captain of Miami Metro Homicide, having been promoted from Lieutenant (with Detective Debra Morgan taking her place) by former Deputy-Chief Tom Matthews. She led almost every investigation in the series, with Sergeant James Doakes and Angel Batista supervising the crime scenes under her, handling the political side while her detectives did the dirty work. It wasn't until Season Seven that she began to display her own investigative work.
While initially being one of the Main Protagonists, she was the second and last Main Antagonist of Season Seven (after Isaak Sirko), following her investigation into the Bay Harbor Butcher Investigation (BHB) while trying to clear the framed Sergeant James Doakes of the crimes committed by the Butcher.
Maria can be seen as a tough, determined woman fighting for power in the political game among law enforcement. Often having a friendly (and sometimes antagonistic) relationship with former-superior Tom Matthews, she always stood out as cold in her rise through the ranks. Putting her work before her life, she kept most of her emotions bottled inside which led detectives such as Debra Morgan to be convinced that she was out to destroy her out of a personal grudge.
She does however display a sympathetic side, one often shown in the shadows as she is forced to do less than honorable acts to push herself further into power. From sleeping with a her replacement's fiancee to marrying and then divorcing a coworker, the toll has been heavy but she never lets it show to those around her. In her early days she was partnered with Sergeant James Doakes and the two developed a close relationship, at one time being lovers and staying close friends for many years. Even as the rest of the Miami Metro Police Department and even the FBI closed in on him as the suspect behind the Bay Harbor Butcher Investigation, she refused to believe he was guilty and strove to support his innocence (though it was in vain).
This relationship she shared with Doakes was powerful enough that despite several years passing since his death, a discovery of a blood slide at a crime scene led her into investigating the Bay Harbor Butcher again in hopes of clearing his name. It is strongly implied the two were in an intimate relationship, as Doakes was married at one point but was never stated who he was maried to as LaGuerta stated that it was Doakes' anger that drove her away. She has proven to come closer than anyone before her in investigating Dexter Morgan, having uncovered his past and relationship to the Ice Truck Killer as well as strong evidence to support him being the Bay Harbor Butcher.
LaGuerta was very ambitious and politically driven. When she lost her job to Esmee Pascal, LaGuerta began sleeping with Pascal's fiancé Bertrand. Pascal began to become irrational, using department resources to investigate her fiancé and acting out erratically. Pascal was eventually replaced, at which point LaGuerta stopped sleeping with Bertrand. Interestingly, LaGuerta has some qualms about what she was doing; she refused to speak ill of Pascal to Captain Matthews, showing that she knew what she was doing was wrong and that she felt guilty about it.
She is very determined to maintain her position no matter the cost, such as blackmailing Captain Matthews into promoting her. She is also very manipulative, telling Matthews that she would help make the call girls case go away, but instead used Debra by having her dig information on the case that would connect back to Tom and sold him out to the board and had him forcibly put into retirement to gain his position. Even Debra commented on how that was a very low thing she did to Tom and Debra prompting her to ask "How do you sleep at night?!" to which LaGuerta replied "very nicely, knowing that from now on you will do as I say or I'll find someone who will". This shows that she is often more than willing to betray or use anyone to get what she wants, regardless of who she is close to.
Despite her manipulative nature, however, she often shows compassion, loyalty (especially for Sergeant Doakes) and has a strong regard for justice (for instance when she gives defense attorney Ellen Wolf information that proves Chicky Hines innocent, even though she knows that this would strain relations between herself and her former lover, Miguel Prado). She comforts Debra when Joey Quinn was arrested for the murder of Stan Liddy (though later released because of Dexter), telling her to "have faith" and when she was feeling bad about how Travis got away, telling her she did a good job in trying to catch him. She did admit that what she did to Matthews was wrong, but felt it had to be done despite Deb's statements of how she really did it for herself (which was true). She has a strong bond with Dexter during most of the series, most notably in the beginning of Season 5 when she shows her solidarity after Rita's death and even suspends Quinn for trying to investigate him, following her murder. This can also be seen when she gets Dexter to sign the papers for the official marriage between herself and Sergeant Batista and trusts only him as she investigates Miguel Prado for the murder of Ellen Wolf. Her greatest sense of loyalty is towards Sergeant Doakes, whom she is intent on proving innocent (the two are later revealed to have been lovers for a while).
However, LaGuerta is not above making her subordinates feel intimidated. At the series' beginning, she had a sincere dislike for Debra which in later series has all but disappeared. In the first season, she made no secret of her attraction to Dexter, whom she flirted with constantly, to his discomfort (which after the 1st season it has yet been mentioned or suggested and sees him more as a good friend).
Discussions between LaGuerta and Batista in Seasons 1 and 4 give minor insight into LaGuerta's back story; her family is said to reside entirely in Cuba, and she mentions being alone in a strange land, inferring that LaGuerta was sent to live in America, alone (perhaps in foster care?), by her family. Also in Season 1, LaGuerta showed possible interest in adopting a Cuban boy who had been a witness to a crime (inferred by a conversation she had with Debra about Dexter's adoption), but the boy's uncle was located.
It is obvious from the first episode that Maria and Debra do not get along. Maria purposely makes it harder for Deb to get into homicide but eventually has to let her in. At the end of the first season, she is removed from command so her captain can save himself.
Early in Season Two, she continues to struggle with her demotion and annoyance of Esmee Pascal's presence in the office. She resorts to sleeping with Pascal's fiancee Bertrand (though often doubts what she's doing), which quickly drives Pascal toward paranoia and instability. The woman's increasingly erratic behavior around everyone results in Captain Matthews being forced to take her out of the Lieutenant position and put Maria back.
When her friend, former partner and former lover James Doakes becomes the prime suspect in the Bay Harbor Butcher case, she tries to clear his name. She learns from a questionable source of two Special Forces missions Doakes took part in that directly conflicted with the deaths of two Butcher victims. However, Doakes is found dead in a seemingly accidental explosion, along with the body of drug dealer Jose Garza, and the case is closed. The evidence LaGuerta finds is ignored. After his death, LaGuerta starts a memorial fund for him, asking police officers for donations, and refuses to think of her deceased friend as a serial killer.
As she recovers from the trauma of Doakes death, she leads an investigation into the murder of Oscar Prado, the brother of her ex-boyfriend Miguel Prado. She also develops a close relationship with lawyer Ellen Wolf, and is devastated when Wolf is found dead. But through the help of some personal investigation work, along with Dexter's help, she was able to discover that Miguel was the one who killed Wolf and usually confides in Dexter as he is the "only other one who knows". She becomes distraught when the Cuban community is thinking about naming a highway after Miguel and wants to find legal evidence to prove he killed Wolf, but Dexter is able to convince her that doing so would only hurt Miguel's family and the Cuban Community, and even then there is a high chance that won't prove anything and drops it.
At the start of Season Four she is shown to be romantically involved with Angel Batista. They keep their romance hidden from the rest of the staff within the homicide department, aside from Dexter, whom both Batista and LaGuerta confide in. Their relationship hits a roadblock when she tells their superiors about their relationship so that it cannot be used against them during a trial. The consequence of her disclosure is a threat of reassignment; either Batista or LaGuerta will have to move out of Homicide. Deciding that their jobs are integral parts of who they both are, the two decide to end their relationship, and sign affidavits to that effect. Staying away from each other does not prove easy, however, and they begin having secret liaisons once more. In order to circumvent a reprimand from higher up, and also as a result of their deepening feelings for one another, they secretly get married with Dexter as witness.
In Season Five, Maria and Angel are married, but they begin to have problems, as Maria becomes too bossy with him and Angel becomes more impulsive and gets in a bar fight.
Maria has recently divorced Batista after realizing that he's not as politically driven as she is (at least according to Matthews). She is promoted to Captain in the first episode after blackmailing Deputy Chief Matthews over a madam's contact list which includes his name. Chief Matthews assigns Debra Morgan as the new Lieutenant to LaGuerta's dislike, because she promised the position to Batista. He seemingly did it to get back at LaGuerta. Morgan went from being completely clueless and unsure of her new position in the beginning confided greatly in LaGuerta's help, but because of LaGuerta's obvious dislike for her she gives her a lot of bad advice, much of which backfires on LaGuerta. Morgan soon gains enough confidence in her position to not need LaGuerta's advice anymore, and also begins to realize what LaGuerta has been doing.
However, with Matthews' second transgression with a prostitute, she initially tells Debra to cover it up, but when she continues to search and finds proof of Matthews' involvement, LaGuerta disables both Matthews and Debra, with Matthews being called to retire and blackmailing Debra with her coverup. She makes it clear that she will depose Debra if she does not do as she's told.
While Miami Metro Homicide was at the scene of Travis Marshall's murder, LaGuerta found a blood slide. The slide served to fuel LaGuerta's belief that James Doakes was innocent of being the Bay Harbor Butcher. So she decided to try to reopen the case, not only in an attempt to find the true murderer, but to prove the innocence of her departed friend and former partner. She continues to investigate till Debra gains wind of this and decides to help her (and keep tabs for Dexter). As they interview a victims family, LaGuerta sees Debra hiding something about the case and imediately suspects she knows something, but says nothing so Debra doesn't get suspicious herself. As LaGuerta starts reaching dead ends in the case, she eventually digs deeper and discovers a name on several of the cases: Dexter Morgan. This causes her to recall Doakes obsession on Dexter and believes Doakes may have been right.
Her suspicion would prove right as she discoveres that Dexter moved his boat around the time of the case, which causes her to dig deeper into his background. She continues to look into this without Debra's knowledge due to her belief she knows something (which is true). She enlists the help of Tom Matthews on the condition he gets his 40 year pension plan due to her having cost it in the first place. She tells him of her suspicion about Dexter being the BHB and how he has a boat and Doakes never did. The visit the site of Doakes's death at the cabin. Once there, they gain word that the cabin was owned at the time of Santos Jimenez, which Matthews remembers the name as he was responsible for murdering Dexter's mother, Laura Moser, prompting LaGuerta to realize Dexter had more of a reason to kill him than Doakes. This would be fueled even further after hearing that Dexter's brother, Brian, was the ITK and that the BHB chops there victims into pieces and the Jimenez is missing, having been killed by the BHB, causes LaGuerta to imediately believe Dexter to be the genuane BHB and that Doakes was on to him. She attempts to question him constantly, but Tom stops him stating he'll do it since he's knows Dexter since he was a kid and he trusts him much more.
After Tom talks with Dexter over Dexter claiming Doakes had a boat, LaGuerta refuses to listen, stating his feelings for the Morgan family is clouding his judgement and if Doakes had a boat she would have known about it. They still look into this boat business and find a key in a tackle box from the cabin that leads them to a deserted boat stand and find several sheets of plastic. They call a private forensics team and find knives in a closet, one of which that has blood degraded on it and a finger print on it that is Doakes's. Tom is convinced this is more than enough, but LaGuerta still isn't convinced and believes Dexter planted this (which is true) and could have done all this, but Tom still wants her to stop this as it's over and nothing more can be done stating he's done with all this. LaGuerta is saddened by this, but promises Tom his pension plan like they agreed.
However, it turns out she still wasn't convinced and still plans to go after Dexter, having pushed for Hector Estrada, the man who ordered the death of Dexter's mother, out on the streets after 40 years in prison. Dexter was almost about to kill him in the kill room when Estrada reveals LaGuerta being the one who pushed for his release. LaGuerta arrives on scene with two officers and hear a chainsaw going on in a storage container and enter to see the room full of plastic and LaGuerta orders the two men to find Estrada and that he's not alone. She looks into the room further and believes further that Dexter is the BHB.
In previews for the next episode, LaGuerta is seen arresting Dexter (likely due to the Estrada incident) but not with enough evidence. It seems she's forced to let him go after Debra arrives and demands to know why she's trying to frame Dexter prompting LaGuerta to yell that he's the BHB and he has to be, which has Debra walk off. However, LaGuerta still refuses to back off.
In the season finale LaGuerta discovers more evidence about Dexter's true identity and on top of that, the warrants to track their GPS on the date of Travis's death. Her discoveries lead Dexter to the only decision logical for him - kill her. His plan is to set LaGuerta up by first killing Hector Estrada and then killing Maria, while making it look like Maria and Estrada killed each other. His plan goes smoothly until Deb walks in minutes after Dexter tranquilized LaGuerta. Because LaGuerta was given less than the usual tranquilizer Dexter gives to his victims so that the M99 wouldn't be found in her blood she wakes up in the middle of Dexter and Debra's dialogue. She tells Debra that she needs to kill Dexter, but in the end a very emotional Debra shoots LaGuerta and kills her.
- Her characterization in the show departs significantly from that in Darkly Dreaming Dexter, in which she is a shrill, manipulative woman whose only real objective is promotion within the department. Another departure from the books is that LaGuerta died near the end of the first book after being stabbed by Brian upon discovering Brian and Dexter standing over a restrained Deb. A sample of her blood is also taken by Dexter for his blood slide collection following her death.
- LaGuerta was antagonistic towards Debra Morgan for a majority of the series, usually providing an obstacle in her path to advancement in Miami Metro. It wasn't until Season Six that the two began to understand one another further and they were on good terms throughout a majority of Season Seven (with Deb being the only one trusted with LaGuerta's investigation into the Bay Harbor Butcher).
- Ironically, despite LaGuerta becoming one of the two Main Antagonists of Season Seven, it wasn't Dexter who killed her but Debra herself. This proving to be the only time one of the lead characters dealt with one of their own main antagonists apart from Dexter (the other in this season being Joey Quinn with George Novikov).
- LaGuerta is the second main antagonist of season 7 as well as second female antagonist to appear in previous seasons.
- Strangely, her body is positioned in exactly the same fashion when she was first unconscious (due to m99) and after Debra shoots her.
- Despite being an antagonist for many different portions of the series, she was never a "bad" character, justice-wise. While some of the actions she performed were less than honorable, ultimately she sought justice in her own ways, apart from taking over Matthews's position. In Season Seven her actions were to try and clear the name of an innocent man while finding the actual killer and arresting them. Her antagonistic role was that of an opposing force to the lead title character, one that he had to overcome. It is understandable as Dexter has always been a villain protagonist instead of a 'good' one.