“Dexter” introduced several unforgettable serial killers, including the main character, but none captured as much attention as the Ice Truck Killer. Dedicated to his wicked ways, Brian Moser (played by Christian Camargo) takes the lives of at least 20 victims while assuming the alias Rudy Cooper, before meeting his end at the hands of Dexter Morgan (portrayed by Michael C. Hall) in the first season. Dexter, in true fashion, eliminates the Ice Truck Killer by replicating Moser’s own method of murder—slashing his throat and hanging him upside down to drain his blood until he dies.

The story delivers an additional surprise when it is revealed that Brian is actually Dexter’s biological brother. Like Dexter, he witnessed the horrific murder of their mother by Santos Jimenez (portrayed by Tony Amendola). However, unlike Dexter, Brian was not guided by a figure like Harry Morgan (James Remar) who instilled a sense of justice. Without any moral guidance, Brian succumbs to his dark urges, killing for enjoyment and trying to lure Dexter onto the same malevolent path.

Ultimately, Brian’s ambition to form a serial killer duo with his younger brother is permanently thwarted. Dexter refuses to become what Brian has, despite his love for him. Faced with Brian’s atrocious actions, Dexter condemns him to death, suppressing his emotional turmoil. Yet, as fans know, the world of “Dexter” is anything but straightforward.

Brian is an innocent kid, deeply attached to his little brother, when he and Dexter witness their mother’s murder. Unlike Dexter, he is incarcerated in a mental hospital instead of being adopted. Harry finds and rejects him, noticing a darker streak in him than in Dexter. While hospitalized, Brian’s desire to hurt others only festers, though he learns to behave like a normal, honest person. 

After aging out of juvenile detention, Brian drifts for a period as he takes up serial killing, swiping the identity of a man he murders, Rudy Cooper. All the while, he stalks his brother, getting closer and closer to him. He moves in on Dexter’s adoptive sister Debra (Jennifer Carpenter) — whom he secretly loathes for taking Dexter away from him — eventually making her his fiancé. But all he wants is the old connection he had with his little brother, and he’ll do anything to reestablish it. 

Brian goes too far in kidnapping Debra, hoping to talk his brother into killing her together and thus symbolically shedding his adoptive personality and identity. Instead, Dexter lures Brian into coming to his home, firmly rejects his idea of brotherly love, and kills him, leaving his blood-drained body to look like a suicide. It’s one of the show’s most jaw-dropping moments, even for Dexter himself, providing the series with one of its best episodes.

Dexter is the only mourner at Brian’s funeral. He considers this such a loss that he doesn’t take a souvenir slide of blood, as he typically does with all of his murder victims. But a younger version of Brian (Roby Attal and Xander Mateo) actually has a strong presence in “Dexter: Original Sin,” a prequel series which examines his brother’s earlier years.

During that show’s run, Dexter is on his first case, investigating the “N.H.I. Killer,” another alias pinned to Brian while he was in his early days as a murderer. While Dexter himself develops his moral code and keeps killing, Brian is on his own sad trajectory toward death and mayhem that’s completely different from that of his bro.

It’s Harry who begins to realize that Brian is the serial killer they’ve been hunting. Unfortunately, that means facing the boy he rejected, leading to an untimely confrontation. While Harry can’t rescue Brian from his fate — nor Dexter from his — he does try. But the brothers are destined to be rivals, in both slaying and in life. It’s only Debra who proves to be Dexter’s ultimate breaking point — and his reason for clinging to his humanity in spite of it all.