The Sensorites were a timid yet scientifically advanced people who feared humans coming to their planet, the Sense Sphere. Although very unassuming in their appearance – short, dressed in grey, with bulbous, bald heads and tufts of white hair – the Sensorites were capable of telepathy and used this to communicate with Susan. A mysterious illness was killing many of their population and had begun after they were visited by a human space crew. The First Doctor solved the mystery of the illness and helped rebuild Sensorite-Human relations.