Summary

• Key characters like Deb and Brian discovered Dexter's dark passenger, leading to dramatic confrontations and secrets revealed.
• Dexter's adoptive father, Harry, gave him a moral code for killing, but ultimately couldn't handle the monster he created.
• Other characters like Isaak, Lumen, and Vogel played significant roles in Dexter's journey as a vigilante serial killer.

Although Dexter's killer protagonist was always careful not to get caught, there were a number of key characters who find out about Dexter Morgan’s dark passenger over the course of the series. Dexter documents the life of Dexter Morgan, a vigilante serial killer who also happens to be the blood-spatter analyst for the Miami Metro Police Department. Dexter operates his serial killing unconventionally, sticking to a strict code where he can only kill those who deserve it — confirmed murderers who have evaded the justice system.

While trying to appease his dark passenger’s need for blood, Dexter has to carefully avoid getting caught while on the hunt and after he kills. His most important rule while serial killing is to not be caught, which means not letting anyone know his real identity or acting in a way those around him find suspicious. Aside from his many victims that obviously knew Dexter was a dangerous killer in their final moments, only a select few established characters found out about Dexter's dark passenger. From loved ones to adversaries to new allies, these characters discover his darkest secret.

Harry Morgan

Played By James Remar

After finding him in a pool of his mother’s blood in a shipping container, police officer Harry Morgan adopted Dexter as his own son. As Dexter grew older, Harry noticed abnormalities in his son, especially his interest in blood, withdrawn demeanor, and need to kill animals. Realizing Dexter would either need to be institutionalized or likely end up in prison for homicide, Harry decided to use Dexter’s killer affinity for good.

Once Dexter killed his first human being (an evil nurse), Harry gave Dexter the “Code of Harry,” which outlined Dexter’s rules for killing.

Once Dexter killed his first human being (an evil nurse), Harry gave Dexter the “Code of Harry,” which outlined Dexter’s rules for killing, including not getting caught and only killing murderers who escape justice. During this time, Harry had been seeing a therapist who helped “create” Dexter into the vigilante he was, before it all became too heavy of a burden.

After physically seeing Dexter murder and chop up one of his victims, Harry became physically sick. Knowing what he created in Dexter and what he had seen, Harry Morgan ended up committing suicide.

Debra Morgan

Played By Jennifer Carpenter

In one of the most memorable moments of his secret being revealed, Dexter's adoptive sister Deb learned Dexter and Harry had hidden his serial killing from her all her life. Even as an adult, when Debra was Dexter’s closest connection, he could never tell her because he didn’t want to burden her with the knowledge and figured that, as a cop, she would feel the need to turn him in. Finally, in Dexter’s season 6 finale, Debra happened upon Dexter murdering The Doomsday Killer in his ritualistic fashion at the church.

At first, Deb didn’t know Dexter was a serial killer and only tried to help cover up his apparent one-time murder.

At first, Deb didn’t know Dexter was a serial killer and only tried to help cover up his apparent one-time murder. As season 7 progressed, Debra found out that Dexter was a methodical serial killer and that their father helped guide him, causing her to be physically ill. Because Deb loves Dexter so much, she still helped hide his identity, even when it led her to make the life-altering decision of killing Maria LaGuerta.

The guilt of committing a murder of her own ate away at Deb until she eventually reconciled with Dexter. After going into a coma due to a gunshot wound, Dexter euthanized her in an act of love.

Brian Moser (Ice Truck Killer)

Played By Christian Camargo