Doctor Who follows the adventures of the primary character, a rogue Time Lord from the planet Gallifrey, who simply goes by the name "The Doctor". He fled from Gallifrey in a stolen Mark I Type 40 TARDIS – "Time and Relative Dimension in Space" – time machine which allows him to travel across time and space. The TARDIS has a "chameleon circuit" which normally allows the machine to take on the appearance of local objects as a disguise. However, the Doctor's TARDIS remains fixed as a blue British Police box due to a malfunction in the chameleon circuit.