Clone

A clone was, usually, a genetic copy of another biological entity. Clones could be produced to be exact replicas with short lifespans, as the Fourth Doctor did for himself and that of Leela at the Bi-Al Foundation, (TV: The Invisible Enemy) or they could be clones of individual cells which were grown into a usable organism, as Cassandra O'Brien did for herself following the destruction of the skin taken from the front of her body, on Platform One. (TV: New Earth)

Military use
The Sontarans were a clone race, making each Sontaran almost identical to the other. (TV: The Invasion of Time, The Sontaran Stratagem)

Clones of Gallifrey were created during the War in Heaven against the Enemy and came to be known as Nine Gallifreys. (PROSE: The Shadows of Avalon, The Book of the War)

On Moldox, during the Last Great Time War, the Daleks cloned Kaled mutants for their paradigm of Temporal Weapon Daleks armed with Temporal Cannons. (PROSE: Engines of War)

As part of an attempt to convert Earth in the 26th century, the Cybermen harvested genetic material from captured humans in their conversion bases and began growing human clones that could be converted to effectively double the Cybermen’s numbers. (AUDIO: Machines) In an alternate timeline, another army of Cybermen launched a full-scale invasion of 24th century Sontar to acquire the Sontarans’ cloning technology, allowing them to clone and convert an infinite number of Mondasians. The Tenth Doctor speculated that they would replicate this technology across entire planets, using void drives to transform these breeding worlds into spaceships. (COMIC: Supremacy of the Cybermen)

Espionage
A clone of Martha Jones was made by the Sontarans to infiltrate the United Nations Intelligence Taskforce during the Sontaran invasion of Earth in 2009. The clone had a mental link with the real Martha and could access her memories. If the link was broken, the clone would most likely not survive. The Sontarans used many clones to try to stop the Tenth Doctor from interfering with the conversion of the Earth's atmosphere and the subsequent invasion. The Doctor broke the link between Martha and the clone, killing it, but before it died, Martha used the fact that it still had some of her memories to convince it to help them. The clone explained that the ATMOS gas was clone feed. (TV: The Sontaran Stratagem / The Poison Sky)

Using blood samples taken from the Sixth Doctor in 2004, the Forge operative known as Nimrod created a multitude of clones in the form of the Sixth Doctor in order to discover the means of Time Lord regeneration. None of the clones could regenerate. They only had a one-in-ten chance of surviving birth and would not live very long afterwards. Nimrod had abandoned this project by the time of the Seventh Doctor's visit to the Forge's base in Dartmoor in 2008. (AUDIO: Project: Lazarus)

The Daleks had the technology to create duplicates of humanoids, employed in undercover work. (TV: Resurrection of the Daleks)

Labour force
Santa Claus used clones of himself to deliver presents on Christmas Eve. (PROSE: The Man Who (Nearly) Killed Christmas)

In the 22nd century, humans cloned Gangers from the Flesh as a workforce in industrial facilities. Most of these Gangers were just remotely controlled rather than independent entities, but some of these Gangers gained free will. Ganger technology continued in one form or another into the 52nd century. (TV: The Rebel Flesh / The Almost People)

In the far future, clones of Wolfgang Amadeus Mozart became hugely popular, not just for their musical talent but also used to perform menial duties. They were abandoned or thrown away after they became unfashionable. One clone time travelled to 1791 Vienna to save Mozart's life and give him immortality, creating an alternate timeline in which Mozart lived long enough to become a hack. However, the clones were still mistreated in this timeline since enough people remembered the good music Mozart had written. The Sixth Doctor negated this timeline by persuading Mozart to refuse the clone's offer and destroying some of the pages of Mozart's final symphony, thus limiting the scale of Mozart's reputation so that the only clones that would be created were those that were genuinely wanted rather than to be part of the fad. (AUDIO: My Own Private Wolfgang)

Other instances
Using DNA from the Fourth Doctor, a clone of the Second Doctor was produced. He believed that he was the Doctor, and even contained memories taken from the Doctor. However, he was in league with the enemies of the Doctor. The Fourth Doctor saved his life and he repaid him by helping return Hexford to its original place on Earth. Like the examples noted above, it was not believed to be able to last longer than a few months. (AUDIO: The Hexford Invasion, AUDIO: Survivors in Space)

A clone of Bernice Summerfield became President of Earth. (AUDIO: The Final Amendment)

Clones of the Three Who Rule were produced. (PROSE: Blood Harvest)

In June 2027, Ace told Henry Noone that Earth would have "new pandas" by 2040, suggesting that pandas had become extinct at some point in the early 21st century and were eventually brought back to life through the use of cloning. (AUDIO: A Death in the Family)

In 2040, efforts were made to repopulate Europe with cloned wolves. (PROSE: Culture War)

Davros created a clone of his younger self named Falkus on Azimuth. (AUDIO: Daleks Among Us)

In 4880, Professor Oksana Kilbracken developed a process of cloning on Earth. (AUDIO: Revenge of the Swarm)

In 5000, a short-lived clone replica of the Fourth Doctor and one of Leela were produced by Professor Marius and shrunken down to fight the Swarm inside the Doctor's brain. When the Swarm took control of Marius, he made a clone of Lowe to pursue them. These clones had lifespans of less than eleven minutes. (TV: The Invisible Enemy)

Professor Patrick Trethui cloned Vilgreth from the remains of a Titanthrope he had discovered. (AUDIO: Last of the Titans)

A planet of Rory Williams clones were populated from Rory's DNA. (COMIC: Planet of the Rorys)

Madame Karabraxos of the Bank of Karabraxos used clones of herself to staff important positions at the bank. When they failed, Karabraxos had the clones "fired", incinerating them. The Twelfth Doctor came into conflict with one of these clones, Ms Delphox, while robbing the bank. (TV: Time Heist)

Madame Kovarian used Melody Pond's embryonic DNA to create clones of Melody. The first seven clones were lost after the Eleventh Doctor's raid on Demons Run. Kovarian created at least four more clones who she raised into adulthood as assassins, to complete the job of permanently killing the Doctor. (AUDIO: The Lady in the Lake, The Furies)

On Kirith, the Grand Matriarch had clones of Ace, Raphael and Miríl created to attack the Seventh Doctor; she killed them when he refused to fight them. (PROSE: Timewyrm: Apocalypse)

Other references
In Pete's World, Angela Price suggested that Cybus Industries had perfected the science of human cloning to explain Ricky Smith's doppelganger, actually his parallel universe counterpart from N-Space. (TV: Rise of the Cybermen)

The Eleventh Doctor likened the process of restoring the universe from a single atom to cloning a body using a single cell. (TV: The Big Bang)

The Aja'ib contained tales involving cloning. (PROSE: Bafflement and Devotion)