"Doctor Who" is a series that thrives on change, so much so that not even its two main characters -- the Doctor and their companion -- can be depended on to stick around for the next season. Even little things fans might take for granted, like the basic shape of the Doctor's sonic screwdriver or the general notion of the Doctor keeping a consistent outfit, can be casually tossed aside at a moment's notice.

The only true constant is the Tardis, the Doctor's trusty blue box that travels through time and space and is somehow bigger on the inside. Appropriately, the term "Tardis" itself stands for "Time And Relative Dimension In Space." It's a term that was supposedly coined by the Doctor's first companion Susan (Carole Ann Ford), but all the Time Lords we'd later see in the show would refer to their time machines by the same name. I...