Giles

Name: Rupert Giles
Place of Birth: England
Type: Human / Watcher
History: Giles was born into a family of Watchers (those who train and guide Slayers) — both his father and grandmother were Watchers. The young Giles was disappointed to find out that he was destined to be a Watcher; he had wanted to be a fighter pilot or a grocer.
He attended Oxford University, but attempted to reject his destiny and instead rebelled and dabbled in the occult with his friends (who called him "Ripper"), at one point summoning the demon Eyghon to Earth.
Giles eventually straightened out and gave in to his destiny, working as a museum curator in England until the Watcher's Council assigned him to Buffy in Sunnydale. Giles, while also working as the Sunnydale High librarian, developed a close father-daughter-like relationship with Buffy, despite the fact that she is an untraditional, somewhat incorrigible Slayer.
Giles doesn't seem to have many friends, though he dated computer science teacher Jenny Calendar (until she was killed by Angelus), had a one night stand with Joyce while both were under the influence of poisoned candy (rendering them like teenagers), and a few passing liaisons with a British woman named Olivia.
Giles is well-read and intelligent, can play the guitar, fence, and read five languages — and, if necessary, he can hold his own in a fight.
Giles has always been fairly straight-laced and stereotypically British, but he has loosened up a bit since he was fired from his post as Watcher (after interfering with the Council's rite of passage test for Buffy).
After the gang graduated from high school, Giles was unemployed for a while, except for guitar performances at the Espresso Pump, but he eventually took over a magic shop, The Magic Box, after the previous owner was killed by Harmony's vampire gang, and turned it into a successful business.
Buffy also managed to bully the Watcher's Council into rehiring him as her official watcher, complete with retroactive pay. After Buffy's death at the end of Season 5, Giles moved back to England.
He returned to Sunnydale when she was resurrected, but later felt that it was best for Buffy if he left, so that she could learnt to be more independent. He did visit at the end of Season 6, in order to help the gang stop Willow, who had gone a bit mad after Tara's death and was trying to end the world.
After this incident, Willow went to stay with him for a few months, to learn how to control the magic now within her.
Although Giles now remains in England, he did come back to Sunnydale towards the latter half of season seven to help Buffy with the Potential Slayers.