Four of these Daleks (Dalek Thay, Dalek Caan, Dalek Jast and a black Dalek named Dalek Sec) escaped the end of the Time War in a void ship along with a captured Time Lord prison ship containing millions of Daleks, which they called the Genesis Ark. They have the ability to extract information from living brains through the use of their suction cups, although this may result in death of the person. The Doctor caused the Daleks released from the Genesis Ark to be sucked back into the Void, but Sec and the rest of the Cult of Skaro managed to initiate an emergency temporal shift to 1930s New York City. The Cult believed they were the last four Daleks in existence.
The Cult of Skaro returned in "Daleks in Manhattan". Operating from a laboratory underneath the Empire State Building, the Cult use "Pig-slaves" to capture people for their experiments. As the last of their race, the Cult's situation became desperate, with Dalek Thay sacrificing his rear casing for construction of a mast at the top of the building. Dalek Sec questioned the genetic superiority of the Dalek race, and proposed the creation of a Hybrid Dalek which they hoped would combine the best traits of both humans and Daleks. In "Evolution of the Daleks", Sec was removed from command by Dalek Caan, before being accidentally exterminated by Thay, sacrificing himself to save The Doctor. The Dalek Humans exterminated Thay and Jast soon after. Dalek Caan destroyed the hybrids and initiated another temporal shift, becoming the last known living Dalek in existence.
In the 2008 episode The Stolen Earth, it is revealed that Dalek Caan travelled to the first year of the Time War, despite it being time-locked. Doing so cost Caan his sanity. However, Caan can make guesses of what will happen in the future, with some of them coming true (for example, the Doctor's arrival). Whilst in the Time War, Dalek Caan rescued Davros from the wreckage of his command ship, allowing Davros to return to the present day and create a new Dalek Empire with his DNA. Davros holds Caan in high esteem, although the new Daleks believe Caan to be an "abomination" due to his insanity and his possession of emotions.
When he passed though time and space to rescue Davros he saw the carnage of the Dalek race. In Journey's End Caan convinced the Half Doctor to destroy the Daleks and end their reign of terror. Dalek Caan and Davros are believed to have been killed when the Crucible was destroyed by the Half Doctor. However, Russel T. Davies confirmed that Davros may still be alive, as he said "I'd never be the writer to kill off Davros".
Dalek Sec was the leader of the cult and the Dalek attack during the Battle of Canary Wharf against the Cybermen. He showed his leadership by communicating to the enemy, namely, Rose Tyler, Cybermen and The Doctor, and commanding the other three Daleks. Because there were only four Daleks outside the void, Sec fought alongside the other Cult members against the enemy, and kept checking the status of the Genesis Ark. However, as soon as the Ark was 'primed' Sec escaped the Torchwood tower with the Ark, to command the entire army of Daleks from the sky whilst keeping a close watch on the Ark. Because the Cyberman Army and the Void Ship containing the Cult, the Genesis Ark, and the Dalek Army within had travelled through the void, they had all picked up 'void stuff' which, when the Doctor reversed the flow of the radiation, sucked both armies, the Genesis Ark and the Void Ship back into the Void. Dalek Sec and the Cult were able to escape the slaughter by initiating an Emergency Temporal Shift.
Along with the rest of the Cult of Skaro, he ended up in New York in 1930 and established a base beneath the Empire State Building. Taking control of the Empire State construction and forcibly converting humans into "pig slaves" to serve as a labor force, the Cult of Skaro also worked on experiments designed to evolve Dalek-kind into a new form. The Cult recruited the power-hungry human servant Mr Diagoras, who seemed to think like a Dalek the most, which Dalek Caan admitted. Sec turned against the concept of Dalek genetic purity, viewing survival as more important and seeing human DNA as holding useful attributes, as the humans thrive as a species whereas the Daleks had become extinct. Using himself and Mr Diagoras as the test for the Final Experiment, he was transformed into the first Hybrid Dalek.
While in his new body, he began to feel humanity for the first time in his existence, being motivated by emotions rather than the traditional Dalek drive to conquer. Motivated by these, Sec asked the Doctor to help him create more hybrids using human bodies, and started to express his feelings that their creator was wrong. He decided to have the new race live on, different from the Daleks, since if they continued to try to be superior, they would eventually die. However, the other Daleks came to reject Sec's theories and eventually betrayed him while Dalek Caan took control and fueled the other human bodies with pure Dalek DNA. When the Daleks tracked the Doctor down, they took Sec with them, putting him in chains and accidentally exterminating him when he saved the Doctor by sacrificing himself. The Doctor showed his respect for Sec by calling him the "cleverest Dalek ever" and the only creature that could have led the Daleks from the darkness.
Dalek Sec made a prediction mere seconds before his death, stating "My Daleks... understand this. If you choose death and destruction... then death and destruction will choose you." Dalek Jast had dismissed the thought at the time, but a mere minute later he was the next of the Cult to die, by the hands of the Human Daleks. Dalek Thay was also killed at this time.
It is worth noting that, due to his hybridisation from Dalek to Human Dalek, Dalek Sec has been the first Dalek to repent the deaths he caused, and the only Dalek who willingly sacrificed himself to save the Doctor.
His character as a Dalek/Human hybrid is not entirely clear, as, although he eventually feels humanity, it is sometimes also implied that he still had plans to cause destruction. An example would be when Dalek Caan becomes 'controller' of the Human Daleks; Sec responds to this act of treachery with "That was to be my position!"
When he was a Dalek, the mutant inside Sec had longer tentacles than other previously seen mutants, and was able to engulf Mr Diagoras in a sack-like membrane projected from what appears to be his mouthparts.
According to the Doctor Who Files book on the Cult Of Skaro, Dalek Sec was the Commander of the Seventh Incursion Squad and led the attack on the Mechonoids on Magella before being promoted by the Dalek Emperor.
When the Daleks arrived in 1930s Manhattan, Caan had a far more significant role. He oversaw the construction of the Empire State Building, delivering orders from Sec to Mr. Diagoras and acting as the Cult's contact on the surface, as well as abducting people in the sewers. After Sec's transformation into a Human Dalek, Caan and Jast begin to doubt their leader's motives. When Sec decides to give the Dalek Humans emotions, Caan mutinies, altering the process to make them 100% Dalek. Caan overthrows Sec and takes command of the Cult. When the Dalek Humans, influenced by Time Lord DNA the Doctor had introduced into their genome, kill Daleks Jast and Thay, Caan self-destructs them all. Dalek Caan's voice also changed dramatically from its original deep baritone to a pitch matching Dalek Sec.
The Doctor confronts Caan and offers to help him, stating that he is not willing to commit another genocide so soon after Dalek Caan's. He coldly informs Caan that he is probably the only one in the universe who would show Caan any mercy. Caan's only response is to initiate another Emergency Temporal Shift, escaping once more, although the Doctor remains convinced that he and Caan will meet again.
Dalek Caan reappears in "The Stolen Earth". His Emergency Temporal Shift somehow brought him into the time-locked Time War, allowing him to rescue Davros, the creator of the Daleks. During this rescue mission, Caan "died a thousand times" and most of his casing was badly damaged. The stress of this — along with the almost-impossible feat of navigating himself into a "time-locked" event — destroyed his mind, but also allowed him to witness "all of time", effectively making him precognitive. Other Daleks can be heard referring to Caan as 'The Abomination' — a title also given to the Special Weapons Dalek in the novelisation of Remembrance of the Daleks, and to Rose Tyler, having absorbed the power of the Time Vortex in "The Parting of the Ways". Caan is the first Dalek seen to laugh (albeit insanely) in the BBC's revival of Doctor Who; however, it should be noted that the humanised Daleks in the classic series serial Evil of the Daleks are also heard laughing. Nicholas Briggs, the voice of the Daleks, claimed to do a sing-song voice when portraying Caan at this point, to hint that he is now 'bonkers'. Davies described Briggs' portrayal of Caan as "the creepiest Dalek yet".
Though he appears to guide the Daleks with his prophecy, he in fact leads them to their deaths. Having seen the whole of time, he saw the Daleks for the evil they represented, and helps the Doctor to destroy them. It was he who orchestrated the events that brought Donna Noble and the Doctor together (twice) to eventually bring them to this point in time (he insists that he merely "helped" and the events would have happened regardless), creating the more violent clone of the Doctor which would be willing to do the job. In effect, though he originally betrayed Dalek Sec after the latter's merging with a human, Dalek Caan has made the prediction Dalek Sec made shortly before his death come true: the Daleks chose death and destruction when they created the Reality Bomb, and through Dalek Caan's planning and interference, death and destruction claimed them. Caan and Davros are left on board the Crucible as it explodes, apparently killing the both of them. Just before the Doctor leaves, Caan reiterates that one of "them" will die; although not a literal death, this may refer to the Doctor's companion Donna: the Doctor is forced to wipe her memories to save her life, "killing" the adventurous and knowledgeable Donna but leaving behind the one he first met.
Like the other regular Dalek members of the Cult, he had doubts about Dalek Sec's plan to merge with a human as part of Sec's vision of Dalek "evolution". He sacrificed 3 panels of his skirt to create the lightning conductor of the Empire State Building. In the climax of "Evolution of the Daleks", Thay inadvertently exterminated the Hybrid Dalek Sec, who sacrificed himself to save the Doctor's life. Thay was destroyed (along with Dalek Jast) when the Dalek Human hybrids rebelled against the orders to kill the Doctor and opened fire on the Daleks instead.
According to the Doctor Who Files book on the Cult Of Skaro, Dalek Thay was the Commandant of Station Alpha, the most secret Dalek research facility, before being promoted by the Dalek Emperor.
Jast and Thay assisted Sec in experiments underneath the Empire State Building. When Sec was about to merge with Mr. Diagoras and become the first Human Dalek, he and Thay intervened with Sec's experiment in order to maintain Dalek purity, but Sec retorted that their road for supremacy has brought the Daleks to extinction. Jast continued to question Sec's motives, and eventually betrayed him along with Thay and Caan. He was destroyed by the Dalek humans along with Dalek Thay by the weapons of the human Daleks.
Dalek Jast had the highest-pitched voice in the Cult. He was the second member to be exterminated, shortly followed by Thay.
According to the Doctor Who Files book on the Cult Of Skaro, Dalek Jast was Force Leader of the Outer Rim Defensive Battalion before being promoted by the Dalek Emperor.