A TARDIS is a product of the advanced technology of the Time Lords, an extraterrestrial civilisation to which the programme's central character, the Doctor, belongs. A properly maintained and piloted TARDIS can transport its occupants to any point in time and any place in the universe. The interior of a TARDIS is much larger than its exterior, which can blend in with its surroundings using the ship's "chameleon circuit". TARDISes also possess a degree of sentience (which has been expressed in a variety of ways ranging from implied machine personality and free will through to the use of a conversant avatar) and provide their users with additional tools and abilities including a telepathically based universal translation system.