In all of Dalek history there are few individual Daleks save perhaps the Emperor himself who can claim to be as important or influential as the Cult of Skaro, as they are some of the most interesting Dalek characters ever created and were the first Daleks to reappear across multiple episodes. These four Daleks were created by Russell T. Davies for the Series 2 finale Army of Ghosts / Doomsday and went on to become the first individual Daleks to have names and unique personalities.

We are introduced to the Cult of Skaro during the climactic cliff-hanger ending of Army of Ghosts and their names and personalities are expanded on more in Doomsday, in which they are revealed to have escaped the Time War in a Void Ship along with a mysterious Time Lord artefact called the Genesis Ark. These four Daleks are capable of imagination, something that most standard Daleks lack, and as such they are able to out-think their enemies and made exceptional tacticians during the Time War.

Each member of the Cult can be identified in several ways. The first and most difficult way of identifying each member is by their unique tag located underneath their eyestalk, as in theory each Cult member has an associated tag that is printed onto their prop. Unfortunately, however, during filming of the two main episodes in which the Cult of Skaro appear, the props were routinely switched up, sometimes even between shots, so this method is all but useless in practicality.
The easiest way to tell the Cult members apart is by their voices, as Dalek voice actor Nicholas Briggs gave each member of the Cult their own unique voice and personality. Dalek Sec has a standard Dalek voice with an authoritative tone, Dalek Caan’s voice is very deep and rasping, Dalek Thay has a low-pitched voice with a nasal croak, and Dalek Jast has a high-pitched, staccato voice with a very fast line delivery.

Who is Dalek Jast?

Jast is perhaps the least developed member of the Cult, as he has the fewest lines of the group and does not get any notable scenes on his own. He is the Dalek that first notices that the Doctor is present at Torchwood by analysing the communication with the Cyber-Leader, and he is seemingly the one in charge of directing where the Genesis Ark should move.
Dalek Jast’s greatest claim to fame is assisting Dalek Caan in the aerial attack on Hooverville in Evolution of the Daleks, and then later accompanying Dalek Thay to the theatre where he is later killed by the Human-Dalek hybrids. Jast is identifiable by his high-pitched voice and fast, energetic line delivery. Dalek Jast’s reserved nature is due to more than just Nick Briggs wanting to minimize the amount of squeaky Dalek dialogue, however, as Jast comes across as one who only comments when he feels his eye for detail is necessary, to voice a concern that the other members of the Cult may have missed.
Who is Dalek Thay?

Thay is the most prominent Cult member early on, as he is the first of the group to be introduced by name and is also the Dalek that starts the war with the Cybermen in Doomsday. He is identified by his medium-pitched voice that has a distinct nasal croak, and he is often the first Cult member to speak his mind during group discussions.
After starting the war with the Cybermen, Thay doesn’t do much for the rest of Doomsday, but he becomes prominent again in Daleks in Manhattan as he is the Dalek who sacrifices his three back panels for the Final Experiment, making him the only Cult of Skaro member other than Sec who can be easily identified from a distance.
After spending most of the two-parter skulking around in the sewers, Dalek Thay accidentally kills the hybrid Dalek Sec before being destroyed by the Human-Daleks. Overall, Dalek Thay is quick to voice his mind and also quick to fire his weapon, and this more often than not ends up getting the Cult into fights, either with the Cybermen or with the Human-Dalek hybrids, which eventually ends up getting Thay killed.

Who is Dalek Caan?

Caan gets only one line in Doomsday, his booming announcement of his own name. As the Cult member with the deepest voice, Nicholas Briggs chose to limit Caan’s lines early on when voicing the Daleks, but in Daleks in Manhattan / Evolution of the Daleks Caan becomes more prominent.
He is the Dalek who liasons with Mr Diagoras on behalf of the Cult, and in Daleks in Manhattan he laments that his planet has been destroyed and that the Daleks must now look to the Humans for inspiration. It seems as though he is in favour of the Final Experiment at first, as he does not participate in the debate before Sec absorbs Diagoras and he later gives the speech about the Daleks needing to evolve in the climax of the story before the Hybrid emerges.

Caan clearly begins to show doubts about Sec, and he even asks Dalek Thay if he shares those feelings in a great little scene between the two in one of the sewer corridors. The two Daleks guiltily swapping treasonous thoughts in what passes as a Dalek whisper illustrates how the Cult members are more individual and less drone-like than standard Daleks. Caan eventually takes over the Cult when the other members deem Sec to be inferior, designating himself Controller.
Dalek Caan’s voice changes from deep to high-pitched when he takes on the role of Controller in Evolution of the Daleks, as Nicholas Briggs wanted to take advantage of Caan’s new role to justify a voice change. Dalek Caan was given a guttural, rasping voice in Doomsday because he had only one line, but Briggs began to find the voice difficult to maintain after the extended conversations between Caan and Diagoras followed by a speech Caan gives to Martha and the other Humans in Daleks in Manhattan.

After being left as the final surviving Cult member at the end of Evolution of the Daleks, Caan goes insane when he rescues Davros from the Time War. Seeing the Daleks for what they truly are, Caan betrays Davros by instigating the fall of the New Dalek Empire in Journey’s End.
Who is Dalek Sec?

Arguably the most famous member of the Cult of Skaro, Sec is immediately recognizable because of his jet black casing that sets him apart from the other Daleks. Sec is the one who exchanges verbal quips with the Cyber-Leader over the comms in Doomsday in an iconic scene which illustrates his razor-sharp wit and sense of humour, which is unusual for a Dalek, even a high-ranking one. After losing the Battle of Canary Wharf, Sec and the other members of the Cult travel to 1930s’ New York and there Sec merges with the Human Diagoras and becomes the Dalek Sec Hybrid.

Evolution of the Daleks deals with Sec coming to terms with his Human emotions following his transformation, and he eventually develops into a kind and pacifistic man who genuinely wants to save the Daleks from their constant cycle of death and destruction. The other Daleks see Sec as impure, however, and betray him. Sec is demoted and treated as little more than a pet by the Daleks, but he continues in his efforts to convince them to change their ways. In the end, Sec sacrifices himself to save the Doctor’s life by standing in the way of a blast from Dalek Thay that was meant for the Doctor, proving in the end that he was a good man despite his Dalek nature.
Before his death, Dalek Sec tells his Daleks that their efforts to spread death and destruction will inevitably turn against them, and he is proven right mere minutes after his death as the remaining Human-Dalek hybrids choose to turn against their masters and destroy Dalek Thay and Dalek Jast, leaving Dalek Caan as the last surviving member of the Cult.
Why were the Cult of Skaro created?

According to Dalek Sec during his conversation with the Doctor in Doomsday, the Cult of Skaro was created by the Emperor in the latter years of the Time War to ensure the survival of the Dalek race at all costs by imagining new ways to survive. This explains why Dalek Sec is willing to go to such extreme lengths during the two stories in which he appears as he risks corrupting the timeline by invading 21st century London, and then he chooses to alter Dalek DNA during the Final Experiment.
The creation of the Cult of Skaro proves how desperate the Dalek Emperor was getting towards the end of the Time War, as the Cult are given authority above anything within the existing Dalek hierarchy and Dalek Sec uses this authority to justify the radical alterations to Dalek DNA during the Final Experiment. The other members of the Cult are less convinced that Humans are a species that Daleks should learn from, but we already know that the Emperor himself reached the same conclusion.

The Daleks created by the so-called ‘God of all Daleks’ that we see in Bad Wolf / The Parting of the Ways are created from cells harvested from Human bodies, and the Dalek Emperor builds an entire army of impure, Human-bred Daleks that he uses to invade Earth. Whilst the Emperor is clearly insane, it is interesting to note that Dalek Sec and the Emperor both reach similar conclusions of how to perpetuate the Dalek race.
What Happened to the Cult of Skaro?

Following the disastrous Final Experiment, three members of the Cult of Skaro were dead and the last surviving member of the group, Dalek Caan, was sent hurtling into the Time War by his own Emergency Temporal Shift. Caan intended to rescue Davros and save the Dalek race, but in the process of falling through the Time War the last member of the Cult of Skaro saw his race for what they were – genocidal killers.
Caan chose to rebel against the Daleks and eventually brought about the downfall of Davros’ new Dalek Empire by tricking his creator into gathering the Doctor and his friends on the Crucible to ensure the Daleks’ destruction. Caan was presumed killed during the destruction of the Dalek Crucible but Davros suffered the same fate and was later revealed to be still alive, leading many to question if Caan did truly die.

Whether Caan died in the fires of the Crucible or not, it is safe to say that the Cult of Skaro itself is dead. Their ultimate goal was to out-think their enemies by imagining, but unfortunately their imagination made them enemies of each other. Both Dalek Sec and Dalek Caan both individually reach the conclusion that the Dalek way of life is wrong, and the two members of the Cult who remained loyal Daleks to the end, Thay and Jast, were destroyed by their own hubris.
The Cult of Skaro arc is probably one of the most insightful Dalek storylines both for fans and potential writers for the show, as it not only delves into an interesting aspect of Dalek lore, but it also illustrates the folly of the Dalek race as each member of the Cult is destroyed by their efforts to either uphold or influence Dalek doctrine.
Why did the Cult of Skaro fail?

Although Dalek Thay and Dalek Jast make the point that the Final Experiment was contrary to Dalek doctrine and would ultimately have weakened them, the fact that the other Daleks in the Cult of Skaro chose to use their powers of imagination to rebel against Sec exposes the fatal flaw in the very concept of the Cult of Skaro, in that four Daleks with the power to imagine will inevitably turn on each other when any one of them imagines something a bit too far outside the Dalek sphere of thought.
The ultimate tragedy of the Cult of Skaro is that the only two Daleks of the four to actually utilize their imagination to the extent that they break free of Dalek conditioning only manage to do so once they are corrupted in the eyes of other Daleks. Dalek Sec becomes a compassionate man by fusing his DNA with Humans but is cast out by his comrades as a result. Dalek Caan learns the truth of the Dalek race but in doing so is blinded and deemed an insane abomination by the Supreme Dalek.

Into the Dalek would later give us a natural evolution of the Cult of Skaro, the essence of the two best Daleks of the Cult galvanized into one Dalek. Rusty experiences similar epiphanies to Dalek Sec and Dalek Caan, in that he learns the value of humanoid life and also fosters a growing hatred of other Daleks. However, Rusty retains his Dalek casing and weapons, and is able to not only rebel against his own kind but also establish his own sanctuary on Villengard, slaughtering any Daleks that come to destroy him.