Maria LaGuerta

Lieutenant María LaGuerta is a tough, determined woman in command of the Homicide division. At the series' beginning, she had a sincere dislike for Debra which in later series has all but disappeared.^[2] In the first season, she made no secret of her attraction to Dexter, with whom she flirted constantly, to his discomfort. After the first season, however, it is suggested that she sees him more as a good friend. At the end of the first season, she is removed from command.^[3]
She returns to her old job once the new Lieutenant, Esme Pascal, proves to be unstable (a state LaGuerta intentionally worsens by having an affair with Pascal's fiancé).^[4] When her friend and former partner and lover, James Doakes, becomes the prime suspect in the Bay Harbor Butcher case, she tries to clear his name. However, Doakes is found dead in a seemingly accidental explosion along with the body of drug dealer Jose Garza, and the case is closed. 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 defense attorney Ellen Wolf, and is devastated when Wolf is found murdered. After Miguel's own murder (ostensibly at the hands of The Skinner, but in reality by Dexter), she wants to find admissible 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 that even then there is a high chance that nothing will be proved. Reluctantly, LaGuerta drops it.
At the start of Season 4, she is shown to be romantically involved with Angel. They keep their relationship hidden from the rest of the homicide department, aside from Dexter, who both Angel 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 Angel 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.
LaGuerta and Batista divorce in between seasons 5 and 6.
In season 6, Captain Matthews is promoted to deputy chief and LaGuerta is promoted to fill Matthews' position. It was later disclosed that LaGuerta had blackmailed Matthews in order to become the captain. LaGuerta wanted to install Angel Batista, whom she can trust, to be the new lieutenant of homicide division, but as a payback to LaGuerta, Matthews appoints Debra Morgan to be the new lieutenant instead. Later in Season 6, when Matthews was involved in a prostitute's overdose death, LaGuerta used Debra Morgan to keep the case alive and eventually leaked the information to the police chief, who forced Matthews to retire. It was implied LaGuerta would become the next deputy chief.
At the onset of Season 7, LaGuerta finds the blood slide of Travis Marshall at the scene of his death. Remembering that this is the MO of the Bay Harbor Butcher, she then launches an independent investigation as to whether the Butcher was still active and James Doakes was innocent. In Season 7's finale, LaGuerta finds out Dexter is the Bay harbor Butcher, and arrests him. Dexter, anticipating LaGuerta's move, made it look as though she was framing him as the Butcher. LaGuerta then finds more evidence of Dexter and Debra's involvement in the death of Travis. She is eventually killed by Debra, with a shot to the chest, who finds her and Dexter in a shipping container as Dexter was trying to frame her for the murder of the killer of Dexter's mother, Hector Estrada.