The Sensorites possessed bulbous heads with large black eyes and whiskers around their mouths. They were sensitive to loud noises and feared the dark. They were capable of surviving in the vacuum of space. They appeared almost identical even to themselves.
The next-door planet, the Ood-Sphere, contained a dominant life form that is not entirely dissimilar - the Ood.
Early in their history, the Sensorites worshipped the Zilgans, since they lived in the darkness that they feared. They would feed them criminals and would be left on their own. The Doctor accidentally arrived on the planet in a cave of a Zilgan. He was able to kill it. When the Sensorites learned of this, they planned to kill him. With the help of Tony and Amy Barker, he was able to scare them off by shouting and was able to escape.
In the 28th century, an exploration mission from the Earth Empire made contact with the Sensorites and attempted to exploit their world's mineral wealth. The humans appeared to die when their spacecraft exploded and the Sensorites began to suffer a plague shortly afterwards.
Years later, when a second exploration mission from Earth arrived, the Sensorites feared they would also attempt to exploit them and held them prisoner aboard their ship. The situation was resolved by the Doctor and his companions, who made peace between the Sensorites and the Humans, and revealed that the plague was actually atropine (or nightshade) poisoning caused by the insane survivors of the first expedition.