Krillitane

The Krillitanes were a race that could take physical features from races they conquered.

Biology
The Krillitanes were able to take the abilities from other species, giving them new appearances and qualities. They could also create morphic illusions, giving them the appearance of yet other species.


 * When the Doctor first encountered them, the Krillitane looked like humans with very long necks. (DW: School Reunion)
 * In 1140, the Krillitanes were in the initial stages of their bat-like forms, having only recently conquered Bessan and, as such, had hooked tails and longer necks. This gave them the impression of the devil to the human natives of Earth at the time. The Krillitane oil had become toxic to them by this point. (NSA: The Krillitane Storm)
 * In 2007, the Krillitanes had become more human-like, with shorter necks and smaller tails. They had various shades of skin ranging from pinkish to charcoal gray, sharp claws and a flattened, fanged face. They slept upside down like bats and had very sensitive hearing. The Krillitanes were carnivorous and would eat other sentient creatures, but they would also eat rats. (DW: School Reunion)
 * In 2007, Lassar became completely human, but shared the original Krillitane's carnivorous habits. (DW: School Reunion)

Krillitanes also produced Krillitane oil. (DW: School Reunion, NSA: The Krillitane Storm)

Culture
Krillitane apparently referred to each other in familial terms. Toeclaw was known as Brood-Mother (NSA: The Krillitane Storm), while Lassar was known as Brother Lassar (DW: School Reunion).

History
10 generations before 2007, the Krillitane conquered Bessan, killing millions. They took bat-like wings from the inhabitants. (DW: School Reunion)

In 1140, Lozla Nataniel Henk attempts to breed Krillitanes in Worcester, but was defeated by the Tenth Doctor. By using their own oil against them, Henk attempted to create a huge, mutated Super Krillitane that he could sell to the highest bidder as a weapon. However, the creature was killed when Captain Darke threw a vial of Krillitane Oil into its mouth as it was rampaging around the city of Worcester. (NSA: The Krillitane Storm)

In 2007, a group of Krillitanes led by Brother Lassar landed in Deffry Vale in London. They took over Deffry Vale High School, disguising themselves as the teachers. Using Krillitane oil and an advanced computer network, they were using the brains and imagination of the students as a type of computer in order to work out the Skasis Paradigm. The Tenth Doctor, Rose, Sarah Jane and Mickey were able to stop them. (DW: School Reunion)

Lassar was apparently able to survive the defeat, but was trapped in human form. When the Doctor was put on trial by the Shadow Proclamation, Lassar served as prosecutor. "Lassar" was later revealed to be a Gizou named Lau'Tan, who had taken on Lassar's human form as a disguise. (IDW: Fugitive)

Behind the scenes

 * Krillitanes were originally called Krillians, until a check revealed that this was the name of a real computer company. (DWDVDF 7)
 * Russell T Davies' original concept for the Shadow Proclamation scene in The Stolen Earth included an appearance by several swooping Krillitanes, but his plans to feature a "rogues gallery" of alien races in the scene fell through; ultimately the Judoon were the only returning race featured.