Dalek duplicate

Dalek duplicates, also known as Dalek replicants, were humanoid agents created by the Daleks. (PROSE: Dalek Combat Training Manual) Biological duplicates were genetically engineered soldiers conceived as copies of individuals killed by the Daleks, to be used in undercover work. Despite this, the duplicates retained some memories, leading them to fight their programming. (AUDIO: Enemy of the Daleks) In other instances, androids were constructed to serve as duplicates. (COMIC: The Dalek Project, AUDIO: The Fearless: Part 4)

Biology
Duplicates were incredibly strong and were able to perfectly mimic voices. Among some issues with replicants were their cold skin (AUDIO: The Genocide Machine) and eye colour, which the Daleks could never get right. (AUDIO: Daleks Among Us) Duplicates emitted a magnetic field. (COMIC: The Dalek Project)

Pre-Time War
Scrutinising their history, the Time Lords' understood that the Daleks developed the technology to create humanoid robot duplicates that could infiltrate their enemies' ranks. In time they also pioneered a method of producing biological humanoid clones that were conditioned to be loyal to the Daleks. A device that reversed the principles of the robotising machine was used to record brain impulses. (PROSE: Dalek Combat Training Manual)

During their Mechonoid Incident of the First Doctor, Pursuer-Daleks constructed a robotic duplicate of him within their time machine before dispatching him to "infiltrate and kill" the crew of the TARDIS. His memory out of date, this duplicate was exposed when he referred to Vicki Pallister as "Susan" and subsequently destroyed in a fight with the Doctor and his companions. (TV: The Chase)

During the Second Dalek War in the 26th century, the Daleks used a duplicate of Captain Zenna to infiltrate the Cathedral of Contemplation to enable their invasion. (AUDIO: Out of Time)

Briant Michel was revealed to be a Dalek replicant. He had created Taming the Exxilons, a depiction of the Exxilon Gambit which was condemned at the time of its unveiling for the glorification of the Daleks. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)

Propaganda distributed by the Daleks falsely claimed that the members of the United Earth Parliament, including the President herself, were Dalek replicants so as to undermine their authority. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)

By one account, the Daleks' use of duplicates was a recent development in the Dalek-Movellan War, in the aftermath of the Movellan Incident, which did not exist during their earlier conflict with the Space Security Service. (AUDIO: The Dalek Defence)

On Bliss, the replicants gained a reputation. (AUDIO: Enemy of the Daleks) In direct retaliation for the Time Lords' interference in the genesis of the Daleks, (PROSE: Dalek Combat Training Manual) the Supreme Dalek planned to use a duplicate of the Fifth Doctor to assassinate the High Council of Gallifrey, but he escaped before the duplicate was completed. Davros converted some of the duplicates to his own cause and they were all killed off in the crossfire between his Daleks and those loyal to the Supreme. The Supreme Dalek vowed to create more duplicates and invade Earth, though the Doctor insisted that there were unstable. (TV: Resurrection of the Daleks) The Time Lords later believed that these duplicates had indeed broken down, but did consider the possibility that events in Earth's history had been manipulated to serve the Daleks' ends. (PROSE: Dalek Combat Training Manual)

Daleks used copies of the Fifth Doctor and Nyssa to create a virus to wipe out the people of Mojox. (AUDIO: Dalek Soul)

The Daleks created duplicates of Thals for their research on Thaleks. A replicant of Tamarus was destroyed by the Thal-Daleks. Dalek Duplicate technology was crude. (AUDIO: Brotherhood of the Daleks)

According to an unsubstantiated report from the Space Security Service archive on Micawber's World, the Daleks, after being defeated in the Dalek-Movellan War, used their duplication program to infiltrate the Movellan forces and sabotaged the power pack production facilities; infecting all new power packs with a virus that connected them to the Dalek pathweb. After a suitable time had passed the Daleks sent a signal through the pathweb which caused the Movellans to turn on each other. The Movellans never recovered from their civil war and were later wiped out by Davros' Imperial Daleks in a conflict which Daleks called the Pa Jass-Gutrik, the War of Vengeance. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)

In Paris circa 1921, the Dalek Time Controller created a duplicate named Adelaine Dutemps from its own DNA. She was ultimately mutated and transformed into a Dalek Time Strategist. (AUDIO: The Monster of Montmartre) Following her death, Dutemps's remains were used to create a new Dalek Time Strategist (AUDIO: Eye of Darkness) that would serve in the Last Great Time War. (AUDIO: The Shadow Vortex et al)

Time War and beyond
During the War, the Time Lords were on alert for duplicates, with all transduction operatives being instructed to conduct additional security checks on any time capsule returning to Gallifrey. (PROSE: Dalek Combat Training Manual)

Following the establishment of the New Dalek Paradigm, the Strategist and Scientist Dalek studied the original conversion procedure of the Robomen, improving and supplanting them with the Dalek puppets, who also fulfilled the infiltration capabilities of Dalek duplicates. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)

In 1915 during the First World War, the Daleks on their saucer fired a missile on a plane piloted by Lord Hellcombe's son, Ralph, and used his remains to create a robotic duplicate of him to convince Lord Hellcombe that the Dalek claimed to be the last of its race had saved his son, and manipulate him for the Dalek Project. However the Eleventh Doctor has turned Ralph to his cause and he destroyed the saucer, killing himself in the process. (COMIC: The Dalek Project)

Upon being brought aboard the Combined Galactic Resistance command ship in the Good Dalek Incident, Aristotle, the Twelfth Doctor was treated with suspicion by Colonel Morgan Blue, under the precaution he could be a duplicate. (TV: Into the Dalek)

Other references
As recorded in the Dalek Survival Guide, an anachronistic monk's habit was found nearby a hieroglyphic record of a Dalek presence at the Great Pyramid of Giza. It was the guide's supposition that the Daleks knew the pyramids to be burial structures and so brought with them a Dalek duplicate of a religious figure, but misjudged the time period. (PROSE: Dalek Survival Guide)

Behind the scenes
Duplicates were first referred to as such in Resurrection of the Daleks, appearing as biological lifeforms. The Robot Doctor seen in The Chase was retroactively identified as another form of duplicate in sources such as Dalek Combat Training Manual, with androids of the same model as Edwin Bracewell being identified as duplicates in The Dalek Project.