A Watcher was a member of the Watchers Council, devoted to tracking and combating malevolent supernatural entities (and particularly vampires), primarily by locating individuals with the talents required to fight such beings and win. More specifically, Watchers were assigned to train and guide Slayers, girls that were part of a succession of mystically powered young women who were destined to face the forces of darkness. Upon a Slayer's demise, her powers were transferred unto a new girl, who was then assigned a new Watcher herself.
Watchers received training from a young age and had to attend the Watchers Academy which Wesley Wyndam-Pryce was the head boy when he attended. Watchers-in-training were often forced to take part in field tests which required them to defeat an enemy. These were often set in controlled setting where a Watcher-in-training was placed in a situation without any information given to them or warning before hand, where they had to fight a vampire or demon by means necessary, similar to a Slayer's Cruciamentum.  A common testing method that lasted for decades involved locking them in a room with a starving vampire. Other tests weren't organized and were merely pre-existing threats in which the Watchers-in-training were tasked with dealing with based on the information the Council had about the situation. This could lead to an oversight on the Council's part if the information were incorrect, as with the Highgate Vampire incident. When it came to theory, Watchers were known to write theses on famous vampires.
Watchers swore sacred oaths that included an oath to protect the innocent. Associations with vampires were shunned and considered a perversion.
According to Wesley, training procedures have changed to some considerable degree since the 70's, with a greater emphasis on field work rather than books and theory. Watchers tended to be well-versed in ancient, supernatural texts and demonology along with possessing a reasonable degree of skill in hand-to-hand combat and linguistics.
As well as a calling, being a Watcher was also a paid occupation.
Training the Slayer
Watchers taught Slayers hand-to-hand fighting skills mostly in the form of martial arts as well as teaching them to use traditional slayer weapons such as crossbows, axes, swords and quarterstaves. Slayers would be trained regularly; either to learn new skills or to maintain their physical well-being.
Rupert Giles often trained Buffy Summers during and after school hours in the Sunnydale High School library and later built in a training room in the Magic Box filled with gym mats, punching bags and throwable weapons that were hung on the wall, such as shuriken and knives. He also would sometimes accompany her on patrol to monitor her slaying and review her technique.
Other than physical capability, Watchers also trained their Slayer's mentality and senses. Giles once required Buffy to hit him with a ball while blind-folded to test her awareness of an enemy and also conducted meditation with stones after Buffy requested he provide her with extra training so that she may become a better Slayer.
The approach to training the Slayer depended on the Watcher as Giles had a lighter manner of treating Buffy, accepting her social life with few conditions. Sam Zabuto employed a stricter attitude towards training his Slayer Kendra, barring her from her family and any form of a social life while teaching her under a handbook which required her to study demon mythology. Buffy on the other hand was not given the handbook as Giles didn't feel she needed it after he met her. Wesley Wyndam-Pryce opted for a more orderly method of planning out strategies and focusing on three key concepts: Preparation, Preparation and Preparation. Sometime after Giles was fired, Buffy and Faith had to receive testing from the Watcher Council's 'shrink' from things like the Rorschach Test and physical examinations to assertive logic and personality tests that asked if they ever wanted to be a florist (which apparently meant crazy).
After the activation of every Potential Slayer, Slayers were free to join the Slayer Organization where they were trained alongside each other. The appeal to gain Slayers was done by a televised advertisement by new Watcher Andrew Wells, who, along with Violet pretended to be the husband of a stereotypical housewife (Violet) who discovered she had became a Slayer and was told about a 'support group' for Slayers. Joining Slayers were then allocated to a specific area or country where they would receive their training under a sole Watcher or experienced Slayer.
- Alexa Landry
- Archibald Lassiter
- Bernard Crowley
- Edna Giles
- Frederich Lichtermann
- Geoffrey Wyndam-Pryce
- Gwendolyn Post
- Laura Kay Weathermill
- Mr. Whiskers
- Roger Wyndam-Pryce
- Rupert Giles
- Rupert Giles' father
- Rutherford Sirk
- Sam Zabuto
- Quentin Travers
- Unidentified Watcher
- Violet's Watcher
- Willem Bryardale
- Wesley Wyndam-Pryce