    Sentence 1: How many seasons did the original Doctor  Who run?    Sentence 2: Occasionally serials were loosely connected  by a storyline, such as season 8 being devoted to the  Doctor battling a rogue Time Lord called The Master,  season 16's quest for The Key to Time, season 18's  Journey through E-Space and the theme of entropy. and  season 20's Black Guardian Trilogy.