Don't judge a 1960s police box by its cover—it's actually a spaceship that travels through time and space. The acronym stands for "Time And Relative Dimension(s) In Space." The Doctor acquired the TARDIS on the terms of "finders, keepers" and it has become the Doctor's most faithful companion. This is possibly the most intimate bond between a man and a box ever seen on TV. Oh, and it's bigger on the inside.