Dexter's adoptive father, now deceased. For the first two seasons of the series he appeared only in flashbacks to Dexter's childhood, having died ten years prior to the start of the series. From season three onward, the dramatic device of flashbacks was replaced with Harry appearing to Dexter as a "ghost," (whether it is really a ghost or a figment of Dexter's imagination is unknown) which gives commentary on/guidance through, all the problems his son faces through out the series.

Harry Morgan was a Detective and highly-respected member of the Miami Police Department, and a close friend of his immediate superior Lieutenant Tom Matthews. In the course of a high-stakes drug case, Harry began an illicit relationship with Laura Moser, Dexter's biological mother, to gather information and evidence on the drug lords in question. As Laura feared, she was discovered and made an example of; she and three others were executed with chainsaws in a shipping container. Her sons Brian and Dexter were left in the container for several days, sitting in two inches of blood, until Harry and a police team recovered them. Harry adopted Dexter, while Brian was sent into foster care. Harry believed that the older Brian would be forever traumatized by the event and was "unsalvageable," but that Dexter was still young enough to be "saved." Eventually, however, Harry realized that the experience had bred in Dexter an innate need to kill.

At first, Harry attempted to manage Dexter's violent urges by only allowing him to kill animals, but he eventually came to the conclusion that Dexter's pathology couldn't be repressed, only controlled: Harry decided to train the boy as a vigilante, to hunt and kill murderers without leaving any clues. Dexter prized these lessons as a means to fulfill his desires with his father's approval, dubbing them the "Code of Harry". Harry's relationship with his biological daughter Debra, meanwhile, was more complicated. She craved her father's approval, but felt that he favored Dexter. (She of course was kept in the dark about Dexter's "training".)

When Dexter was 19, Harry fell seriously ill and gave Dexter "permission" to kill one of his nurses, who was intentionally poisoning him with morphine. A year later, when Juan Rinez, a pimp who was murdering his own prostitutes, was released due to a faulty search warrant, Harry lost his temper and told Dexter he was right in training him. When Dexter killed Rinez, Harry was horrified by the way Dexter proudly showed him the pimp's dismembered body; it was Harry's first actual view of Dexter's "work", and he was ashamed of what he had trained Dexter to do. Harry committed suicide a few days later by deliberately overdosing on his medication, but not before telling Matthews to look after his children. Dexter discovered this in the show's second season, and began to question his father's motives. It was also revealed in season four in a conversation between one of his old CI's and Debra, that Harry had slept with many of his CI's, not just Laura.