After his mother was killed, Dexter Morgan became an orphan at the age of three and was adopted by Miami police officer Harry Morgan. He was also embraced by Harry’s wife, Doris. During his youth, Dexter discovered his urge to kill neighborhood pets. Harry believed it was too early for him to act on those impulses and told Dexter not to give in to them, but Dexter’s desire to kill grew stronger. Harry advised Dexter not to kill innocent people and taught him a set of rules:

  • Most importantly, Dexter must never get caught.
  • Dexter’s victims must deserve to die.

Dexter must always be sure that the killer is guilty, which is why he often goes to great lengths to gather solid evidence that the victim is truly guilty. Harry taught him to have normal human emotions, to behave socially, and to clean up the crime scene after killing the perpetrators. Dexter follows the code to satisfy his “Dark Passenger” (the name he gives to his instinct to kill). However, in the fourth season, he kills a photographer who is later proven to be innocent.