The Master

The Master appeared with the very first episode of the series and is one of the oldest vampires of the world because it at approximately 600 years. He settled in Sunnydale approximately 60 years ago to open the "Mouth of the Hell" and to release the demons of them on the world. An earthquake destroyed a good part of the city in 1937, thus preventing to him from achieving its projects, since the church in which it was was also destroyed by the seism.
The door which it tried to open blocked and it was found imprisoned its stone cage. Incompetent to escape, it is nevertheless able to guide his disciples in search of fresh blood. The Master is useful himself of an intermediary to take again his forces in particular with Luke but this one was made kill by Buffy. The Master replaça his hopes then on the arrival of the "Juste Of Right" the bus prophecy tells that it will take along Tueuse in Hell.

This project having still failed, it sent "the Trio" to get rid of Buffy. The Master still knows and wanted that it thus returns to his sides it sent Darla to bring back it but this was still balanced by a failure. the Master successful however to escape from his "prison" when a young boy, Billy, in the coma, was used as catalyst with the nightmares of the inhabitants of Sunnydale, allowing them to be carried out.
The worst nightmare of Buffy being to see the free Master. But as of the alarm clock of the boy, all returned in the order. Little time after another prophecy predicted that the Master was going to escape, kill Tueuse and to open the "Mouth of the Hell", which it makes a success of but Alex managed to reanimate Buffy because the Master had drunk his blood to him. Buffy faced the Master on the roof of the college and finally succeeds in killing it by ejecting it by the window of the library and while being spit. Of course its disciples tried to bring back it to the life by bathing it in the blood of those which had to attend its ground setting, but Buffy prevented some by crushing the bones of the Master.

Nevertheless it reappeared in the episode "Better wishes of Cordelia" ("The Wish") when this one made the wishes that Buffy never came in Sunnydale. It reigns on the town of Sunnydale which from now on is populated almost completely of vampires and vampirisé Alex and Willow. After a brawl with Buffy of this world, it broke the nape of the neck to him. But as soon as the wishes was cancelled, all became again like front.

bravenet.com