One of television’s most prolific serial killers returns to Showtime this Sunday with the premiere of Dexter: New Blood. Eight years after the largely despised finale of Dexter, Michael C. Hall steps back into the blood-stained shoes of Dexter Morgan, a forensic technician who happens to have a very dark passenger. Based on the books by Jeff Lindsay, Dexter was a huge hit for Showtime from 2006 to 2013, landing two dozen Emmy nominations, including one for Hall five times in a row and a nod for Best Drama four times in a row. For the new iteration, only one other performer from the original series has been announced to return, with Jennifer Carpenter once again playing Debra, Dexter’s sister. Of course, fans may be confused given that Deb died in the series finale, but Dexter has a habit of staying in touch with people who have passed on.

With most of the familiar faces from Dexter gone and the show relocated from Florida to the Pacific Northwest, what matters now for those considering jumping back in is the history of Dexter himself. How did he get here? What events from his past might haunt his present? These are the key things to remember about Dexter Morgan, the serial killer with a code.

The Birth of a Serial Killer

Most of Dexter’s past isn’t revealed until the end of season one, in which a crucial event becomes a reoccurring flashback for the rest of the series: the murder of his mother. Dexter was born in 1971 to a single woman named Laura, who was a police informant for an officer named Harry Morgan (James Remar). Laura was brutally murdered by drug dealers in 1973, and Dexter and his brother Brian were left in a crate, surrounded by their mother’s body parts. Brian went into the system and eventually became season one’s Ice Truck Killer (Christian Camargo), another serial killer who Dexter is forced to eliminate, but Dexter was adopted by officer Harry. The image of baby Dexter sitting in his mother’s blood returns on every season of the show, suggesting that this is when Morgan’s “Dark Passenger” was born.

Harry Morgan and the Code

Harry recognized early in Dexter’s life that the boy had an urge to kill, teaching his adopted son a code to keep him, and arguably the world, safe. Harry’s code, which, it’s revealed in season eight, was developed with a doctor named Vogel (Charlotte Rampling), has two strict rules: One, Dexter must be certain that his victim is guilty, using his skills as a forensic technician to prove it. Two, he must not get caught. The code also serves dual purposes for Dexter, appeasing what he calls his “Dark Passenger,” the part of a serial killer’s psyche that demands that a life must be taken, while also cleaning up the mess left by the truly inept police officers of Miami Metro. If justice can’t be delivered through legal means, Dexter will take it with his own hands.

Debra Morgan

While the first season of Dexter portrayed a man who knew how to fake typical societal roles like boyfriend, colleague, and brother, his relationship with Debra, a Miami Metro police officer for most of the series, became an emotional through-line all the way into the new series (where she will replace Harry as Dexter’s twisted conscience). Debra and Dexter increasingly bordered on codependency, even as he stayed one step ahead of her in terms of keeping his secret, at least until the end of season six, when Deb caught Dexter committing one of his murders. She was forced to take this knowledge to its horrible end in the close of season seven, killing Maria LaGuerta (Lauren Vélez) when she figured out Dexter’s secret, before really spiraling in season eight from the guilt. She ended up a victim of a serial killer named Oliver Saxon, the son of the doctor who helped Harry with the shaping of Dexter’s code.

The Job of a Serial Killer

The Dexter writers often pitted Morgan against serial killers who murdered without Harry’s code, leading to a series of face-offs over the first few seasons, starting with the Ice Truck Killer. In season two, Dexter’s problems shifted to a sociopath named Lila (Jaime Murray) and a fellow officer named Doakes (Erik King), who figured out Morgan’s secret; they both end up dead, the latter framed for Dexter’s many crimes.

In season three, Dexter partnered with assistant district attorney Miguel Prado (Jimmy Smits) to clean up the streets, but his new partner violated the code before the season introduced another serial killer named the Skinner (Jesse Borrego) to complicate things further. Season four, the show’s best, introduced the Trinity Killer (John Lithgow), who would shape Dexter’s life more than any other. Season five charted Dexter’s redemption through a vengeance arc of a victim named Lumen (Julia Stiles); season six introduced Colin Hanks as the Doomsday Killer; and season seven brought Hannah McKay (Yvonne Strahovski) into the fold (more on her later). The disastrous final season centered on Rampling’s Dr. Vogel and her serial killer son.

According to estimates, Dexter Morgan has killed 138 people, a number likely to rise in New Blood.

Rita Bennett

When the series began, girlfriend Rita Bennett (Julie Benz) was essentially part of Dexter Morgan’s disguise as a human being, allowing him to hide in plain sight. Physically and sexually abused by her ex-husband Paul (Mark Pellegrino), Rita sees Dexter as a refuge, drawn to his seemingly nonconfrontational nature. When Dexter framed Paul to get him sent to prison, where he’s killed in season two, Rita started to suspect something was up with her boyfriend, but he gets her off the scent by faking drug addiction. That led to an affair with Lila and a near break-up between Rita and Dexter, but they reconciled near the end of season two. At the start of season three, Rita discovered she was pregnant with Dexter’s child, and the two married at the end of that year. The fourth season started with Dexter and Rita trying to parent their son Harrison but ended with the Trinity Killer murdering Rita, leaving Dexter a single father.

Hannah McKay

In season seven, Dexter met a gorgeous woman named Hannah, a serial poisoner whom Dexter planned to kill but ended up having sex with instead (it happens). A Bonnie and Clyde for the Dexter series, they helped each other commit crimes, but she pushed the code, killing a writer who learned her secret but had committed no crimes of his own. Debra started to suspect Hannah, turning their dynamic into a bizarre triangle. (It’s even suggested, in one of the series’s low points that Debra is literally in romantic love with her brother.) Dexter picked his sister, giving Debra the evidence that led to Hannah’s arrest, but she escaped from prison, reuniting with Dex in season eight. The pair planned to run off together, but when Debra died, Dexter decided that everyone around him ends up in a coffin and left Hannah to skip town on her own with Harrison in tow.

Harrison Morgan

Harrison and Dexter share a very dark past, both having witnessed the deaths of their mothers in childhood. After Rita’s murder, Dexter juggled his job, fatherhood, and satisfying his Dark Passenger while also growing concerned that Harrison may inherit the broken part of his family tree. It probably doesn’t help that Harrison’s trauma was surely amplified when he was kidnapped by the Doomsday Killer in season six, and never mind that his stepmom is a serial killer, too. In the end, he was taken to Argentina by Hannah. If any living character is going to return from the original series to New Blood, Harrison feels like a safe bet.

Leaving Miami

Where did we leave Dexter Morgan after all this carnage? As Hurricane Laura descended on Miami, Hannah and Harrison flew off to South America, Debra was shot by Oliver Saxon, and Dexter dropped her in the watery graveyard where he left most of his victims over the years. He drove his boat into the storm, faking his death, and is last seen in the Pacific Northwest, miserable and alone.

The Life and Deaths of Dexter Morgan