"If they will not obey then they must die!" - Dalek Thay
Dalek Thay was former Commandant of Station Alpha and later a member of the Cult of Skaro.
Thay along with Dalek Sec, Dalek Caan and Dalek Jast were choosen by the Emperor of the Daleks to become the Cult of Skaro. A secret order, their mission was to think as the enemy think in order to win.
Thay along with the rest of the Cult fled during the last great Time war fought between the Time Lords and the Daleks, thet escaped the war by hiding between realities in a Void ship, along with the Genesis Ark, which contained an army of imprisoned Daleks.
The Cult emerged from their ship in the Torchwood one tower in London 2007, during a Cybermen invaision of Earth. Dalek Thay was ordered by Sec to investigate, and Thay became the first Dalek to encounter the Cybermen. Thay and two Cybermen he encountered both demanded they identify themselves. The two Cybermen tricked him into identifying himself by the Cybermen after both sides refused to 'identify first'. When the Cybermen proposed an alliance, Thay denied them their request and the Cybermen tried to delete him but Thay simply exterminated them both. Thay aided in the awakening process and fought in the following battles against the Cybermen and Torchwood staff to protect the Genesis ark until it opened. However the 10th Doctor a Time Lord and enemy of the Daleks opened the void which sucked the Cybermen and released Daleks back into it but Thay and the Cult escaped with Emergency Temporal Shift which took them to 1930's New York.
With only four of them left, Thay and the Cult had to recreate the Dalek race or they would face extinction. At first they tried Dalek embryo's but they soon died. Sec realized that since humans could survive the Daleks must create a new dalek race born from the combination of human and dalek DNA, a human-Dalek hybrid. Stationed under the Empire State building during its construction, the Cult began to kidnap humans turning the less intelligent ones into Pig Slaves while smarter ones were killed and their bodies were prepared for the final experiment. Thay sacrifised the rear parts of his precious dalekanium attached to the building's mast, being replaced with iron as the bonded polycarbide of the plates was required to attract the gamma strike which would revive the humans as Dalek like. When Dalek Sec decided that he would have Mr Diagoras joined within him to evolve Thay objected to this plan believing they must remain pure Dalek. Sec continued with his plan and became the first human Dalek.
Once alone, Caan asked Thay's opinion of Sec. Thay stated the cult was created to follow Sec but confirmed he had doubts. When Sec sent Jast, Caan and the pig slaves to attack Hooverville, Thay stayed with his leader to oversee the assault via a visual link and noted Sec's reaction to Solomon's extermination and refusal to allow the Doctor be killed by Dalek Caan. Thay later demanded an explanation as to why Sec had spared the Doctor, Sec replied that the Doctor was a genius and the future of the Daleks depended on him. During the creation of the human-Dalek race, Thay rebelled against Sec and the Doctor with Jast and Caan by overiding the gene-feed with pure dalek geneo, when the Doctor discovered this, the cult's remaining pure members revealed their true intentions and threatened to kill the Time Lord if he didn't step away from the controls.
When Sec ordered the cult toobey him, Jast stated that the Doctor was an enemy of the Daleks and Sec was aswell, Thay then justified Jast's statement that Sec had lost his authority by stating he was no longer a Dalek. After the brief argument, Thay ordered the pig slaves to restrain Dalek Sec and the Doctor while the cult monitored the gamma strike for the final experiment, while the Doctor managed to escape, Sec was incarcerated in chains on a nearby wall. When the gamma radiation finally hit and awakened the army of hybrids, Thay proudley declared the accomplishment to his colleques. Once fully awakened, the cult informed the new species of their plans and armed them with Dalek weaponry adapted from "Tommy guns". As the new soldiers spread under Manhatten using the sewer system, Caan pronounced himself the new commander, and ordered that he be connected to the military computer, dispite Sec's protests that the position was reserved for him, to which Thay simply stated that his former leader was no longer fit. As Caan transmitted orders to the Dalek-Humans, Thay monitored the command links to make sure they functioned consistently. During command, Caan later detected a signal from a sonic device, Thay instantly identified the source without the need of any equipment, however he was taken aback that the Doctor had survived the numerous death traps he'd walked into. Thay and Jast were then dispatched to the theatre to face the Time Lord. While confronting the Doctor in the theatre, Thay claimed the Time Lord had to die and was about to fire when Sec, now imprisoned with his chains on Thay's Manipulator arm, threw himself in front of Thay's death ray causing his extermination. After the Doctor explained that the Dalek-humans weren't Daleks and that his Gallifreyan DNA was mixed with their Dalek and human DNA in the "Final Experiment", the Dalek-humans questioned orders and revolted against their Dalek masters. Thay immediately opened fire on the hybrids claiming "If they will not obey then they must die!" Although Thay and Jast exterminated many Dalek-humans in the process, the resulting fire fight destroyed them both.