1. Angelus - Buffy The Vampire Slayer
Buffys first season set the tone for what was to come, but the second is what really kicked the series into gear. Buffy had killed The Master and the general premise of the show had now been established; the Scooby gang had their places, Angel was the back up and Spike and Drusilla would soon arrive. Despite this promising set up for the second season, the show still seemed like it needed something more- some pathos- a personal villain for Buffy. She would soon have one in the form Angelus, the soulless evil alter ego of her boyfriend Angel. Looking back all these years later Angels turn perhaps isnt as shocking as I remember it being, but the impact of it is still there. The change was swift and decisive, when Angel lost his soul, he was gone. There was no eco of what he once was, no sign that deep down he was fighting his evil counterpart. The sick game he played with Buffys mother, the constant threats to her friends and the horrific murder of Jenny Calendar, came together to justify the tragic and memorable end of the season. Though his soul was restored, Buffy was still forced to condemn him to a hell dimension to save the world. He may not have defeated Buffy but Angelus did manage to destroy her innocence, he made a mockery of their relationship, and Buffy didnt even have the comfort of believing he was in a better place. Yes he soon came back, but because of the time differential he had spent an eternity in damnation, and Buffy had to live with the knowledge that she was the one that sent him there. Angelus had a long standing impact on the Buffyverse. In my opinion he stands out as the best big bad in the series and was the catalyst for a large amount of character development for some of the shows big hitters. Whilst Buffy still retained most of the quirkiness that made her such fun, she was never quite the same after this. The death of Jenny led to a dark period for Giles and made the audience believe that at one point, he really could have been the Ripper that we had been hearing about. Most importantly Angel himself became a far more interesting character, as David Boreanaz was given the chance to prove that he could do something other than stand in the shadows and pout. The way that he brilliantly managed to portray two distinctly different characters, showed that he had the star power to carry his own series. It also successfully justified why at times Angel could be such a miserable git. Angeluss flirtations with Drusilla drove Spike to a jealous and vengeful betrayal, and laid the groundwork for his replacement of Angel, when the character was spun off into his own show at the end of the next season.