Rupert Giles, played by Anthony Stewart Head
, is Buffy
on Buffy the Vampire Slayer
. His nickname is "Giles
", and some of his older friends call him "Ripper
Despite being a member of the original cast and remaining on the show all the way up until the sixth season where he was merely a guest star for several episodes, Giles is one of the more underplayed characters of the series. A reason for this is that, as he is forty-something, he's pretty old when compared to the other characters on the show.
Giles' main role in the show is that of Buffy's trainer/guide/protector. As her Watcher, he serves to teach her what it means to be the Slayer, and he tries to protect her and handle the research parts. Giles is like no other Watcher in the past, because Buffy is like no other Slayer in the past - Buffy walks all over Giles. Whereas most Watchers are in full control of their Slayers, Giles is there to help Buffy, not the other way around.
Because of this, and because Buffy lives to be older than probably any Slayer in recorded history, Giles develops a deep emotional attachment to Buffy, which turns into a fatherly care. Because Buffy's parents are divorced, her father is very rarely seen, and Giles seems to frequently take on that role. For instance, Buffy has a tradition of seeing an ice show every year with her father, and when he cancels, she asks Giles instead, and suggests that there's a similarity between a father and a Watcher. It certainly doesn't help that Giles had sex with Buffy's mom when the adults of Sunnydale were acting like kids. And when Buffy's mom dies, Buffy turns to Giles for help, both in raising Dawn, and financially. It is because Buffy turns to him in this time of need that Giles realizes that he must go, because staying there with Buffy is preventing her from growing into the responsible, independent Slayer/woman she should be. With Giles there, Buffy just simply isn't ready to face the world on her own. Giles sings a song about this in Once More With Feeling, and soon after, he leaves Buffy and the gang once and for all.
Because of Giles' care for Buffy, though, they ran into a few problems. On the Slayer's 18th birthday, the Slayer is required to take a test- she is required to defeat a vampire without her supernatural Slayer strength and reflexes. To administer the test secretly, the Watcher must first hypnotize the Slayer and then use muscle relaxants to weaken her. Then he must send her to the testing site and allow her to kill the vampire without her knowing that he is causing her weakness, and without helping her.
Unfortunately, the vampire escaped and captured Buffy's mom, to lure her into his home. She went to Giles, and Giles told her about the test because he didn't want her to go there, and he wanted to protect her. She didn't listen, and in the end, Buffy passed the test and killed the vampire, but she and her mom were about to be attacked by his minion too at that point, except Giles burst on the scene and saved them. Because of his actions, Buffy was very hurt, and Giles was fired from the Watcher's Council for a very long time, until Buffy was able to get him reinstated later when the Council was in great need of her services. In the meantime, Buffy got another Watcher, Wesley, (who she also walked all over), but she still always listened to Giles instead and always treated him as her Watcher.
Unlike the other characters, who, as teenagers, have very little past, Giles' past has been elaborated on quite a bit. When he was younger, he was apparently a rock and roll fiend. This was during the time that he was called "Ripper", and he fell into the friendship of Ethan Rayne, a recurring character who seemed to always cause mischief for Buffy. During his younger days, he dabbled in the ways of magic, as did Ethan. While Giles stayed on some of the safer sides, Ethan eventually got into some of the Dark Magics, and this is where they parted ways. Giles was a rebel, but he wasn't bad at heart, and he chose not to become evil the way Ethan did. Petty theft and smoking is one thing - killing people is something else entirely. It is unclear how or why he joined the Watcher's Council after this.
Giles took over as Buffy's Watcher in the first episode, since her old Watcher (who I'm assuming to be Merrick, from the movie) was killed. He posed as the librarian at her high school, Sunnydale High. He remained there for the first three seasons, until he blew the school up in the third season finale. After that, he went through a long stagnation period where he was pretty lazy and attempted to sing a little bit to reclaim his youthful vigor. Eventually, though, in the beginning of the fifth season, the owner of The Magic Box, the local magic shop, was murdered, and Giles somehow obtained ownership of it. He hired Anya, who absolutely loves money, and she became especially greedy. She sort of pressured Giles to leave when he was preparing to go, because she wanted to run the Magic Box herself. Giles eventually left the store in her hands.
As far as Giles' love life is concerned, there have been two major loves in his life. The first, Miss Calendar, was around for the first and second seasons, until Angel killed her. Giles was very reluctant to forgive Angel for what he did, but he eventually did. Also on his list of conquests is his English friend, Olivia, which was a bizarre relationship to say the least. She was only in a few episodes, and she seemed to be more of a casual sex friend. It was never explained how they got together or why they stopped seeing each other to my knowledge - she was just kind of there, an old friend from England. Part of the uniqueness about her was that she was black, and perhaps this was either an attempt to add some diversity to the show, or to show off Giles' rebelliousness at a time when he was going through a mid-life crisis, or maybe both. Personally, I thought that Olivia was an interesting character that deserved more depth than the writers gave her.
Also, just a note of probably one of the scariest things ever seen in the series - At the end of Once More With Feeling, in the previews for the next episode, it showed Giles telling Anya that he didn't want to leave her, and then he kissed her. This thoroughly freaked out the entire world. Fortunately, this conversation was taken way out of context - the whole group was under a spell that made them forget who they were, and Anya and Giles assumed that as workers in the same store, they were a couple. They were thoroughly disturbed when the spell wore off.
It is interesting, though, that now that Giles is gone, the scoobies just don't seem the same. Where they were more like a close family before, and they were always coming together for meetings with Giles at the head (they always met either at the library, or his house, or the Magic Box), they now seem to be like a loose association of friends. Part of this is because of the turmoil the group has been suffering, but it's also because Giles is what held them together, and what gave them direction. Now they seem to be fighting evil left and right all willy-nilly, with little aim for the future and with little guidance. It's like the scoobies have moved out of their parents' houses for the first time and they're experiencing the real world for themselves, and finding it very hard to deal with. I think I miss Giles almost as much as they do...
Giles' role in the show is not over! He returned for the season six finale when, as he predicted, Buffy would do bad in raising Dawn and Willow's magic would consume her. To prove my point above, when Giles returns, Willow says "Daddy's home".
Giles returns backed by the magic of a coven of witches in England, and he puts a stop to Willow's rampage by giving her a dose of the true nature of magic that gives her a reason to live again (and to let the rest of the world live, but hey, who cares about them?).
So it would seem that Giles is indeed not abandoning his "children", but rather that he is encouraging them to grow. By returning, he fixed Willow's magic problems and somehow fixed Buffy and Dawn's relationship. He ended season six in Sunnydale, but whether he will remain or not remains to be seen.