The Progenitor device was a piece of Dalek technology designed to create new Daleks to prevent the species from going extinct. It stored pure Dalek DNA, and when properly utilised and fueled, could both reproduce fully-grown Dalek mutants and functional battle armour.
Thousands of such machines were created by the Dalek Empire. While the Progenitors would normally activate only to a genetically pure Dalek, they possessed a failsafe where they would activate to entities who were designated as Daleks by the Time Lord who called themselves the Doctor, the greatest enemy of the Dalek race. Over Dalek history however, all the Progenitors were thought to be lost. (TV: Victory of the Daleks)
During the Kotturuh crisis, when the Tenth Doctor had been pressed into an alliance with the Dalek Restoration Empire against the Hond, the Doctor examined a Progenitor aboard the flagship of the Emperor of the Restoration. (COMIC: Defender of the Daleks)
During the Last Great Time War, the Daleks used them to quickly populate the areas of the universe they conquered to make it impossible for the Time Lords to properly cope with their numbers and giving them new fronts to fight. They planned to create a new paradigm of Temporal Weapon Daleks armed with Temporal Cannons that could erase their victims from history. However, the new planned paradigm was never deployed because the Eternity Circle was stopped by the War Doctor and Borusa. (PROSE: Engines of War)
In the era following the Time War, Davros had managed to raise the short-lived New Dalek Empire. However, a single Dalek flying saucer survived the Empire's fall, (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) falling through time to 1941. The three Dalek drones on board, the last three Daleks in existence, detected the signal of the last Progenitor device (TV: Victory of the Daleks) that survived the Time War, (PROSE: A History of Humankind) acquired it, and installed it in their saucer. As the machine did not recognise them as Daleks, the three were forced to rely on the failsafe of the Doctor's testimony that they were indeed Daleks.
To accomplish this, the three Daleks created an android called Professor Edwin Bracewell in London. While one Dalek remained in Earth's orbit with the Progenitor, the other two feigned to be Bracewell's simple robots, called "Ironsides". They eventually tricked Winston Churchill into calling the Eleventh Doctor. After arriving, the Doctor became so confused and frustrated that, in a fit of anger, he struck an "Ironside" repeatedly, addressed them as "Daleks", and briefly recounted his violent history with them. The Daleks transmitted this testimony to the Progenitor, which recognised the Doctor, and duly accepted the command to activate. Shortly afterward, the first five individuals of the New Dalek Paradigm were created. The first action of the New Paradigm Daleks was to disintegrate their three "unclean" forebears, who willingly offered themselves for extermination. The New Paradigm then escaped with the Progenitor through a time corridor to the future and successfully created a new empire, while the Doctor and Amy Pond remained on Earth to defuse the Oblivion Continuum bomb inside the android Bracewell. (TV: Victory of the Daleks)