Welcome to the slayers council
There were many slayers, and still more to be. Most of them have been killed. The only way a new slayer will be chosen is if the old one had died. So you must be thinking "Then why did you say that MOST of them had been killed". The answer to that is that there might be a rouge slayer, one slayer have might only died for a short time and them came back, there are many other reasons. Now there are two present slayers.
Buffy Summers and Faith (only has first name). The reason their are two slayers is because Faith is a rouge slayer. There was also another slayer in Buffy's life time, her name was Kendra. But Drusilla had killed her.
But you cant forget about the watchers. Buffy had 3 watchers, Merrick, Rupert Giles and Wesley. But the only one still with and helping buffy, but no longer her watcher is Rupert Giles.
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But still thats not enough for the slayer. She must have her friends to help her. Buffy's group of friends are called "The Scooby Gang". Members of the Scooby gang are Willow Rosenberg, Alexander Harris, Tara, Riley, Anya. But there used to be more, Angel, Oz and Cordiela Chase. You can't have a slayer without her enemies and vampires.
Here are some extra tidbits you would enjoy:
