Harry Morgan, Dexter's adoptive father and a former homicide detective, was first to spot Dexter's passion for human vivisection and helped his son channel his homicidal impulses into a more constructive pursuit: vigilante justice. Harry is also the person that taught Dexter "the code" of killing people. He has to be absolutely certain that they have done some horrible deeds and "deserve" to die. Dexter often has flashbacks to Harry's lessons. Harry also sometimes appears as a ghost, whenever Dexter is thinking what Harry would've wanted.