Kraals are humpbacked, gargoyle-like humanoids with lumpy grey skin, unusual facial ridges and a rhinoceros-like horn. They generally wear striped tunics.
The Kraal had a wide variety of technological devices, one of the most widely used being their androids. These androids were made in the form of a certain person, generally a Human. They had most of the memories of the subject, but were bullet-proof and loyal to the Kraal. In order to create these androids the Kraal needed to scan the brain of the subject, or someone who had dealt with the subject. This scan was highly painful and could cause brain damage if it went on for too long.
As well as androids, the Kraals also have advanced genetic modification techniques and replication techniques. They could create a deadly virus or recreate an entire village out of the memories gained from a brain scan.
The Kraal lived on a doomed world. Oseidon was getting progressively more radioactive, reaching critical levels. They were able to kidnap a Human astronaut named Guy Crayford and scanned his brain for information. They were able to create many Human-like androids and an entire British village from his memory. After testing these androids, they planned to send them to Earth with a deadly virus to infect and kill all of the Humans. This plan was stopped by the Doctor when he was able to stop the androids with Space Defence Station's radar dish.
The Slitheen family sometimes disguised themselves as Kraals in their attempts to make money.