Following Buffy's run, Whedon intended to launch a television spin-off focused on the character, but rights issues prevented the project from developing.

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.

As the series progresses, Giles increasingly becomes a father figure to Buffy and her friends Willow (Alyson Hannigan) and Xander (Nicholas Brendon).

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.

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".

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.

When new Slayer Kendra Young arrives in Sunnydale, Giles shares with her an appreciation for obscure texts, resulting in Buffy nicknaming her the "She-Giles."

Giles feels betrayed when Jenny reveals she is actually a member of the Kalderash gypsy clan, sent to keep an eye on Buffy's relationship with the vampire Angel.

The Scoobies are given another disturbing glimpse in Giles' past when, along with every other adult in Sunnydale, he reverts to being a teenager by enchanted band candy supplied by Ethan Rayne.

Despite describing the test as "an archaic exercise in cruelty", he secretly injects Buffy with muscle relaxants and adrenaline suppressors, which weaken her significantly, before finally coming clean when the vampire she is meant to fight escapes.

At the beginning of season 5, Giles no longer sees his place in Sunnydale and decides to go back to England, telling no one except Willow, whom he needs to organize the research documents for the Scoobies.

When the owner of The Magic Box is killed by vampires, Giles is convinced by the shop's high profit margins to buy it, hiring Anya as his overly enthusiastic assistant.

Buffy learns that her sister, Dawn Summers, is actually the Key: mystical energy disguised in human form to conceal it from the hell-god Glory.

Despite being overjoyed to have Buffy back, he is furious at Willow for invoking such dark magic, and angrily dismisses her as "a rank, arrogant amateur."

As Buffy begins to rely excessively on Giles for financial and emotional support, he decides his presence is preventing her assuming responsibility for her life.

Giles later loses Buffy's trust somewhat when he takes part in a scheme with Robin Wood to kill Spike ("Lies My Parents Told Me").

As it was too expensive for Anthony Stewart Head to fly out to Los Angeles to guest-star, Whedon created Drogyn the Battlebrand, who was mystically compelled to tell the truth.

He plays a particularly key role in The Lost Slayer series, where a chain of events lead to Buffy (from a point early in the fourth season) being projected into the body of her twenty-four-year-old self in a timeline where Giles was turned into a vampire by the followers of an Aztec bat god, forcing Buffy to face a foe who knows her every technique before she manages to find a way to return to the past and prevent Giles being captured and turned.

Later, as Giles argues that a stalemate is not a solution to the vampire problem, Duncan reveals that in fact the town is feeding the Slayers who come seeking sanctuary to an ancient demon.

[2] After Harmony Kendall's reality show establishes a new pro-vampire, anti-Slayer world order, Faith and Giles are in hiding in the Führerbunker in the "Retreat" storyline.

The group is shocked when Giles comes back to life with all his memories intact, but in the body of a 12-year-old boy due to his Aunts thinking of him as a child during the ritual.

Giles is grateful to be free of Eyghon but furious at the age of his body and they have been trying to bring him back and not stopping a plot by villains Whistler (Buffyverse), Pearl and Nash to mutate humans into a magical species at the cost of a few billion lives.

His youthful interest in witchcraft and sorcery has endured into his adult life; though his natural aptitude for it is only moderate (much less than that of Willow), he does have a high amount of magical knowledge.

Giles is proficient in several languages, including Latin, ancient Greek, Sumerian ("Primeval"), Japanese ("Checkpoint"), and possibly Gaelic ("Fear, Itself"), but weak in German ("Gingerbread"), Mandarin and Cantonese ("First Date").

While his demeanor is typically mild and polite, Giles is not above using raw violence to solve a problem, such as physically threatening Principal Snyder into readmitting Buffy to school after her expulsion ("Dead Man's Party"), pummeling Angelus senseless with a flaming baseball bat and burning down his hideout upon discovering that he had killed Jenny Calendar ("Passion"), manhandling Spike while ordering him to get over his feelings for Buffy ("I Was Made to Love You"), forcing Glory's minion Slook to talk by inflicting a painful-sounding injury offscreen ("Tough Love"), severely beating up Ethan Rayne for information ("Halloween"), and suffocating a critically injured Ben with his bare hands to keep Glory from awakening in his body.

Typically, however, Giles' calm demeanor and professionalism offer him a detached state of authority even in the face of fearsome monsters, as demonstrated during his confrontation with a violent demon in "The Long Way Home".

His moderate proficiency in magic combined with his natural acumen and intelligence still make him quite formidable; in Season Eight's "No Future for You", he kills the warlock Roden, who could fly and conjure easily, through using a spell inventively.

Sophronia and Lavinia theorised that if Giles had been tutored in magic by them rather than being trained as a Watcher at the wishes of his father and grandmother, he would have become an extremely powerful magician, and could achieve this potential in his new life.

However, being a librarian, his occupation requires the use of up-to-date technology and skills to further a library service's goals to serve its patrons efficiently, and in one episode ("Gingerbread"), shows that Giles is proficient with computers at least on a basic level.

An article for The Wrap summarized, "For more than five seasons, the British actor added depth and charm to Joss Whedon's groundbreaking 1997-2003 series as mild-mannered librarian Rupert Giles.