In the fictional universe of the television series' Buffy the Vampire Slayer and Angel, a Watcher is a member of a secret organization of parapsychologists: "The Watchers' Council", which seeks to prepare the Slayer to fight demonic forces. A notable example of a Watcher is Buffy main character Rupert Giles. They are typically modelled after the fictional character Abraham Van Helsing from Bram Stoker's novel Dracula.

Watchers are devoted to tracking and fighting malevolent supernatural entities, particularly vampires, primarily by locating individuals with the talents required to combat such beings and emerge victorious. More specifically, Watchers are assigned to Slayers, girls who are part of a succession of mystically powered individuals destined to confront these foes. Upon a Slayer's demise, the next Slayer is called into duty and assigned a Watcher.

The Watchers' Council trains new Watchers in a private school of sorts. In "Never Kill a Boy on the First Date," Giles implies that Watchers are, to a certain extent, "called" or assigned to become Watchers before attending university. This concept is supported by Watcher families like the Giles and Wyndam-Pryces.

Rupert Giles was Buffy's Watcher at the beginning of the series. It was revealed that he had never been invited to the Watchers' retreat. After being fired by the Council for having "a father's love" for the Slayer in season 3, he remained her unofficial Watcher for the rest of the series. Wesley Wyndam-Pryce became Buffy and Faith's Watcher for a short period. Wyndam-Pryce was fired after Faith turned rogue and Buffy "quit". Rupert Giles was reinstated as Buffy's official Watcher in the season 5 episode "Checkpoint," and he remains so until the events at the end of season 5, though Giles maintains his contacts with Buffy.

A standard Watcher has at least some proficiency in the use of magic, with certain individuals being more powerful than others. One episode in Angel (Sanctuary) reveals that numerous members of the board of directors are alchemists. They are students of demonology and as such have a wide knowledge of various incarnations of evil, but their expertise is usually the vampire. They are also highly educated and can speak a wide variety of languages, both human and demonic in nature.

Watchers are typically well versed in hand-to-hand combat techniques, though they generally confine themselves to training Slayers or supporting them in battles, as their lower strength relatively limits their effectiveness in directly engaging vampires.

In ancient times, a group known as the Shadow Men used magic to infuse a captive girl with the essence of a demon, thereby creating the First Slayer, whom they use to fight demonic forces. The descendants of the Shadow Men go on to form the Watchers' Council.

In 2003, Slayer Buffy Anne Summers uses a strange mystical device to meet with the Shadow Men about the threat she faces from the First Evil, where she learns how the Slayers were created. They attempt to repeat history by infusing an unwilling Buffy with the same demonic essence that they used on the First Slayer to increase her power; however, Buffy refused, as she had come to seek only knowledge, not power, especially if that power meant that she would lose her humanity. After Buffy defeats them, one of the Shadow Men gives Buffy what she wants: knowledge of what is coming. He shows her a vision of the First's army of Turok-Han in the Hellmouth, causing her to start to reconsider her decision, but she is brought back by her friends before she can do anything else.