Kroton (species)

The Krotons were a crystalline race from the planet Krosi-Aspai-Core.

Biology
The Krotons evolved from predatory quasi-organic tellurium based crystals which could mimic their prey's abilities. At some point in their history they encountered a human servo robot and mimicked it, thus attaining semi-sapience. As they evolved they became semi-sentient armoured crystalline beings which fed on and were psychologically linked to mental vibrations. The Krotons had crystalline bodies which could be broken down and reformed to suit the environment and the situation which they were in. (PROSE: Alien Bodies)

Krotons had poor eyesight in daylight and kept the insides of their ships dark. When venturing out in the daylight, a Kroton had to rely on the guidance of another Kroton giving directions through use of a mobile camera. (TV: The Krotons)

Krotons of the Kroton Imperium could alter their bodies into a "combat-shape configuration". More powerful than those the Doctor was familiar with, these Krotons could easily destroy a party of Quarks. (COMIC: The Lost Dimension)

History
According to the Fourth Doctor, the Krotons inhabited a completely different era and region of the universe to the Quarks. Thus, to witness a conflict between the two races would not "make sense". (COMIC: The Lost Dimension)

Early history
The Kroton Absolute were overseen by the First Lattice, originally a fortress on the Kroton's home world. It contained the four highest brains in the Kroton Absolute. The First Lattice was moved from the Kroton home world when the war began with the Metatraxi. It took over four thousand Krotons to lift the First Lattice into orbit and it had exhausted all of them. (PROSE: Alien Bodies)

Encounters with the Doctor
The Krotons encountered the Doctor on at least three occasions. On one occasion the Second Doctor killed a pair of Krotons stuck on a planet of Humanoid slaves known as Gonds. The Krotons had enslaved and manipulated the lives of the Gonds for generations so that they might power a dynatrope (a Kroton spacecraft) with mental energy and escape the planet. The Doctor assisted in the Krotons' destruction with sulphuric acid. (TV: The Krotons)

In his sixth incarnation, the Doctor found a dynatrope on Onyakis with what appeared to be an army of Krotons on board, which had been discovered and reactivated by a group of humans looking for a new source of energy for their colonisation ships. Rather than allow the humans on board the ship to be turned into batteries, the Doctor instead induced a temporary state of hypoxia on the humans already being used, the unstable mental patterns caused by it causing the Krotons to be obliterated by their own equipment. (AUDIO: Return of the Krotons)

The third encounter was on Earth during the auction of the Relic. The Kroton Absolute intercepted a Dalek cruiser on its way to the auction and sent a Kroton of the Daleks' ship in their place. The Eighth Doctor, who attended the auction, was unaware at first of the Relic's origins or of the Krotons' presence. (PROSE: Alien Bodies)

By the 29th century, the Krotons became part of the gestalt that was the Ixtricite, along with other crystalline races. (PROSE: The Fall of Yquatine)

When Pericles Torp was a baby, the Krotons invaded Christmas, attempting to assassinate the Eleventh Doctor to prevent another Great Time War. During the attack, the Krotons destroyed a grain warehouse and several of the villagers hiding inside were killed. The Krotons were eventually defeated by the Doctor, but the loss of life stood as a reminder for the townspeople that he could not save everyone. (PROSE: The Dreaming)

Alternate universes
In an alternate universe, the Krotons, organised into the Kroton Imperium, were the dominant power of their reality, theorised by the Fourth Doctor to be the result of a hypothetical absence of the Daleks. A fleet passed into a gate through the Void to N-Space and engaged in battle with alternate Quarks who had arrived the same way. Discovering the Doctor's TARDIS, they engaged a transmat opposing that of the Quarks to bring it aboard, with the Fourth Doctor and Romana II taking the chance and boarding one ship, which they found inhabited by advanced Krotons, to stop the tug of war. A boarding party of Quarks was transmated to the ship to intercept but was quickly destroyed by the Krotons. Soon after, both Kroton and Quark fleets were attacked by forces of the Ogron Confederation of Planets who, coming from yet another universe, sought to cease hostilities between what they saw as "lesser-evolved species" via the use of deadly force. Ultimately, all three sides retreated to face a crisis in their respective universes. (COMIC: The Lost Dimension)

Other references
In the video game Happy Deathday, played by Izzy Sinclair on the Time-Space Visualiser, a Kroton was among a host of "every single enemy" that the Doctor had ever defeated, who were assembled by the Beige Guardian and pitted against the Doctor's first eight incarnations. (COMIC: Happy Deathday)

When the telepathic Emily Fairfax read the mind of the Hypothetical Gentleman, a Kroton was among the images she saw. (COMIC: Hypothetical Gentleman)

During the Eleventh Doctor's stay on Trenzalore, he would tell stories of his encounters with the Krotons to the townspeople of Christmas, possibly implying that the Krotons were at Trenzalore as well. (PROSE: An Apple a Day...)

Behind the scenes

 * The concept of the Xyloks takes inspiration from the basic idea of the Krotons.
 * Russell T Davies's sketch of the original cut Shadow Proclamation scene from The Stolen Earth seems to feature a Kroton among the crowd of aliens.
 * According to Toby Hadoke, voice actor Roy Skelton chose to give the Krotons a South African accent as a deliberate protest against . (DCOM: The Krotons) Although the accent he used sounds more like a Birmingham accent from the English Midlands.