Rupert Giles (/ˈdʒaɪəlz/) is a fictional character created by Joss Whedon for the television series Buffy the Vampire Slayer. The character is portrayed by Anthony Head. He serves as Buffy Summers' mentor and surrogate father figure. The character proved popular with viewers, and Head's performance in the role was well received. Following Buffy's run, Whedon intended to launch a television spin-off focused on the character, but rights issues prevented the project from developing. Outside of the television series, the character has appeared substantially in Expanded Universe material such as novels, comic books, and short stories.

Giles' primary role in the series is Watcher to Buffy (Sarah Michelle Gellar) in her capacity as vampire Slayer; he is in the employ of the Watchers' Council, a British organisation that attempts to oversee the actions of the Slayer. From youth, Giles was expected to follow the family tradition and become a Watcher, though as a teenager and young adult he rebelled, dropping out of Oxford University to experiment in dark magic and the rock music scene, until a bereavement brought him to his senses. In adulthood, his loyalty to Buffy and her group of friends costs him his job for a time. As the series progresses, Giles increasingly becomes a father figure to Buffy and her friends Willow (Alyson Hannigan) and Xander (Nicholas Brendon). His encyclopedic knowledge, affinity for magic, moderate fighting skills and willingness to kill when necessary make him an asset to Buffy in her fight against the supernatural evils that plague Sunnydale, California.

Following Buffy's conclusion in 2003, Whedon intended to continue Giles' story as a spin-off series, Ripper, which he intended to produce with the BBC. The series was to depict Giles in ghost stories set in present-day England, coping with loneliness as well as figurative ghosts from his own chequered past. Over several years Whedon restated his commitment to the project, though announced it would take the form of a one-off TV movie. Despite Head's availability and the BBC's willingness to fund the project, rights issues concerning the character ultimately led to it not developing further. Canonically, the character's story is continued in the comic book Buffy the Vampire Slayer Season Eight (2007–2011) and subsequent stories. The Season Eight sequel Angel & Faith (2011–) heavily features Giles and utilizes ideas and characters from the proposed Ripper spin-off.

Rupert Edmund Giles (most frequently called Giles) was born circa 1955 in England. His family has worked within the Council of Watchers for at least three generations; both his father and grandmother, Edna Giles (née Fairweather), were also Watchers. As a child, Giles dreamt of being either "a fighter pilot or possibly a grocer", but he soon learned that being a Watcher is a calling, much as being a Slayer is, and Rupert's father explained his destiny to him when he was ten years old (revealed in "Never Kill a Boy on the First Date").

Although the Scooby Gang later joked that he wore tweed nappies as a child, Giles was in fact a rebellious youth, rejecting his responsibility as a Watcher and dropping out of Oxford University, where he was studying history, when he was twenty-one. During this time, Giles claimed to be a founding member of Pink Floyd in order to impress girls (although since Pink Floyd was founded in 1965, when Giles would have been around ten years old, it was not a particularly credible claim), and may have delved into criminal activity (he remarks that hot-wiring a car is "like riding a bloody bicycle", and a psychologically younger Giles has no qualms about breaking into a clothing store and attacking a police officer). He is a talented singer and guitar player (as Head is in real life) which the gang discovered, to their astonishment, when they saw him singing "Behind Blue Eyes" by The Who in "Where the Wild Things Are". Spike also saw him singing "Free Bird" by Lynyrd Skynyrd in "The Yoko Factor".

He began to explore dark magic and befriended a group of young people who delved into the dark arts for fun or money: Ethan Rayne, Philip Henry, Dierdre Page, Thomas Sutcliff, and Randall. Giles gained the nickname "Ripper" during this time. Together, the group summoned a demon called Eyghon, who would possess and eventually destroy Randall. Following Randall's death, Ethan and the others failed to exorcise Eyghon, and Giles accepted his destiny of becoming a Watcher. Before becoming a fully-fledged Watcher, he also worked as "the curator of a British museum, maybe the British Museum" as Willow says ("Welcome to the Hellmouth"), although, given the context, she may well have been repeating a rumor that was going around the school.

At the behest of the Watchers' Council, Giles travels to Sunnydale, California, and works as the librarian at the local secondary school. There he meets the current Slayer, Buffy Summers, whom he begins training. The library, a quasi-command centre for Buffy's demon-hunting gang, sits right above the Hellmouth.

As the Watcher, librarian, and general authority figure, Giles often delivers exposition. He is a father figure to Buffy and her friends Xander Harris and Willow Rosenberg, together forming the "core four" of the Scooby Gang. Giles is often portrayed as something of a "straight man" and his "stuffy" Oxford sensibility serves as counterpoint to the stereotypical Southern Californian characters and setting. He makes a "weird cluck-cluck sound with his tongue" when he is angry but is "too English to say anything" ("Faith, Hope & Trick"). He admits to being technophobic, a fact which often brings him into conflict with technopagan and computer science teacher, Jenny Calendar. However, after Jenny aids him in casting the demon Moloch out of the Internet, the pair reach an understanding and begin a romantic relationship. Despite his obvious fear with modern technology, Giles is quite adept with computers, which is required in his occupation as a librarian (season 3 episode "Gingerbread") and likely had received this training while earning his master's degree in library and information science. It was never revealed of which library school Giles attended or whether he had pursued his PhD in this field.