Kroton (species)

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

Biology
The Krotons evolved from predatory quasi-organic tellurium based crystal 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 camera. (TV: The Krotons)

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 sulfuric 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 incarnation of the 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)

Other references
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)