Russell T Davies was an expert in seeding season arcs in small and expert ways throughout his tenure as chief writer on Who - the Torchwood arc in the second season leading to a Torchwood-centric finale; the dropping of hints of lost planets and the Medusa Cascade across a season and a half for series four; and the Master's reintroduction as PM Mr Saxon in the third series. Best of all is the first series' introduction of the mysterious 'Bad Wolf' arc, appearing scrawled on doors, walls, streets and even the TARDIS wall at one point and seemingly without purpose. With the season one finale taking place on an entertainment satellite owned by the Bad Wolf corporation, the arc was resolved with stunning effect when it's revealed that the Bad Wolf was in fact a time paradox message from a supercharged Rose Tyler. She's the Bad Wolf, in a manner of speaking. Rose, easily one of the most beloved companions, is on form here as she becomes the 'Time Goddess' RTD promised, destroying Dalek fleets and resurrecting Jack Harkness to the point where he becomes immortal. She's a brilliant, golden-energy-fuelled force of nature that becomes truly incredible and even lives to tell the tale. One hell of a woman.