The first season of Dexter set up the entire story that would later be continued in Dexter: New Blood. And some pivotal moments are most memorable.

With the sequel series Dexter: New Blood having ended and fans still reeling from the shocking turn of events, it's the perfect time to look back at the show that started it all. Dexter, which aired from 2006 to 2013, had fans reconciling their sympathy for a serial killer with the fact that he was indeed a murderer.

With the story having progressed so much through the seasons, it's easy to forget some of the most pivotal moments from the first season that truly shaped the vigilante serial killer's journey.

The Ice Truck Killer

The first major antagonist of the show was the Ice Truck Killer, a formidable enemy who not only caught Dexter's attention as someone who fit The Code, but also someone who taunted Dexter like no other.

Going by the name of Rudy Cooper, he found his way into the inner circle by dating Debra and spent his days working in prosthetics. He spent much of his youth in a mental institution, diagnosed with Antisocial Personality Disorder. His run-ins with Dexter were an exciting part of season 1. Fun fact that only die-hard fans know about Dexter: the part of the Ice Truck Killer was almost played by Jeremy Renner.

Dexter's Blood Slides

Most serial killers like to keep mementos of their crimes, whether it's a lock of hair, a personal item from each victim, or even something more sinister. In the case of Dexter, it's a single blood slide, which he fills with a drop of blood taken after slicing each victim's cheek.

Fans were introduced to these slides in the first season, along with Dexter's ritualistic practice whereby each was carefully captured, stored, then placed in a box that he hid behind the vent. It isn't until season 2 that the first box is found by the FBI.

Introduction Of The Code

Fans learn all about Dexter and his way of life in the first season, which is also when they first learned about Harry's Code. After discovering Dexter's dark side when finding him killing animals, Harry was left in a precarious position. He wanted to get his son help, but also saw a potential solution that could be good for both of them.

As the flashbacks show, Harry reluctantly taught Dexter to harness his murderous urges by painstakingly vetting his victims to ensure they were "deserving" of death. Harry helped by providing the names of known criminals who managed to skirt the law. It added another layer of complexity to the story.

The Tension Between Dexter And Doakes

Of all the characters who came close to capturing Dexter, Sergeant James Doakes was the most formidable opponent. He was the only one to see through Dexter's façade and realize that he wasn't the sunny, personable co-worker he was working so hard to convince everyone he was.

From following him secretly at night to see what he was up to, to the questioning side looks and the constant threats that he would catch Dexter in the act one day and be proven right, the cat-and-mouse story between the two was exciting.

Rudy Dating Debra

Every serial killer-type show has one of those situations where the killer is right under law enforcement's nose, but they don't see it. This was the case with Rudy, who found a way to charm Debra and begin dating her, marking one of the greatest betrayals on Dexter. This also gave him access to Miami Metro and got him closer to Dexter, which was Brian's reason all along.

The fact that Dexter chose Debra over Rudy (AKA Brian) in the end proved that while Dexter was a serial killer, he had some capacity to feel and/or love.

The Doll Head In The Refrigerator

Before The Ice Truck Killer was identified, and when the murders first started happening, Dexter got a shock when he came home to find a severed Barbie doll head in his refrigerator, mirroring a recent murder.

It was clear the Ice Truck Killer was either someone who knew Dexter or knew what he was up to and was playing games with him. This made Dexter even more determined to solve the case before Miami Metro did and was a catalyst for the eventual showdown between the two.

Dexter's Attempts To Be Normal

One of the best and most unique parts of Dexter is his internal monologue, a strategy that has since been used by other shows, like Netflix's You. In fact, this is just one way You's Joe Goldberg is like Dexter.

One particular scene, however, that never gets old, is when Dexter walks fans through his daily ritual. It's a mundane set of activities he partakes in, day in and day out, in order to keep himself focused and his Dark Passenger hidden. It begins with the iconic opening sequence of the show as he makes the same breakfast of ham and eggs each morning and continues with bringing donuts to the office, greeting everyone with a smile, and engaging in witty banter with Masuka.

Dexter Reliving The Shipping Yard Massacre

It was in the first season that fans learned of the Shipping Yard Massacre and the origin of Dexter's personal trauma. As a baby, he witnessed two drug kingpins murdering his mother, Laura Moser, chopping her to bits with a chainsaw.

Dexter and, he later learned, his brother Brian, were left to sit in their mother's blood for two days before being found. Dexter had blocked the event out of his mind for a long time, but it deeply affected him. Later in the series, Dexter's wife Rita would be murdered in the bathtub, their son Harrison left to sit in her blood in a similar fashion, in one of the most shocking deaths on Dexter.

Rudy Revealed As Dexter's Brother

This was the big twist in season 1 is one that changed the course of the story forever and further indicated just how deeply Dexter had repressed the memory of his mother's brutal death. For some time, Dexter completely forgot that he had an older brother who was also at the shipping yard with him.

While Harry, the first officer on the scene, scooped Dexter up to safety and decided to adopt him, he believed Brian to be too troubled and opted not to adopt him as well. Brian later went searching for Dexter, killing Dexter's biological father Joe in the process, along with a plumber named Rudy Cooper so he could assume his name.

Dexter's Relationship With Rita

Part of Dexter's attempts to appear "normal" was finding a nice woman and having a relationship with her. Dexter chose Rita in part because of her detached behavior.

Since Rita had issues connecting and being intimate with others, it worked perfectly for Dexter, as he was fine with her lack of affection. Seeing him navigate that relationship, trying to pick up on social cues and act like he cared when he often didn't, was fascinating. Still, there was a tenderness about it that suggested Dexter did care, in some way, about both Rita and her kids.

NEXT: 10 Times Dexter Tried To Be Scary (But Ended Up Being Scary)