Rupert Giles was the Watcher assigned to supervise Buffy Summers. Born in 1954. In his youth, he attempted to evade his destiny, and became involved in criminal and occult activities. During this time in his life, he was known as "Ripper" and was friends with the wizard, Rayne, Ethan. After accidentally summoning the demon Eyghon, Giles changed his ways, parted from his old friends, and embraced his life as a Watcher.
In 1997, Rupert was assigned as the new Watcher for the current Slayer, taking as his cover the job of the Sunnydale High School librarian. The two became much closer than most Watcher-Slayer partnerships, with Giles becoming more like a surrogate father to Buffy than a simple mentor. Giles fell in love with a techno-pagan named Jenny Calendar, but she was slain by Angelus upon the his return to evil. This left Giles with a hatred of the vampire that only slightly dimmed when Angel regained his soul.
Rupert Giles was stripped of his Watcher status after he ruined the barbaric coming-of-age ordeal given to Buffy by the Watcher's Council, in showing his fatherly affection for the Slayer by trying to assist her. He was replaced by the woefully inexperienced young Watcher Wesley Wyndam-Price, but continued to unofficially serve as Buffy's mentor. After Sunnydale High was destroyed and Buffy went to college, Giles tried to make a new life for himself. However, he continued to help the Slayer whenever she needed him, up until her death sealing the portal opened by Glorificus.
Giles returned to England for a time, but returned quickly after he learned that Willow had resurrected Buffy. While he stayed in Sunnydale long enough to bring some stability back to Buffy's life- for example, providing her with some funds to support Dawn and herself- he left when he realized that Buffy was becoming overly dependent on him. He returned again, empowered by the magical might of a whole coven, to help stop a power-mad Willow, before returning once again to England with her. Along with the coven, he helped Willow come back to some semblance of normality over the course of the following summer.
After the destruction of the Council of Watchers by agents of the First, Giles returned to Sunnydale along with the surviving potential Slayers. Although he was briefly suspected of being the First in disguise, he helped Buffy take care of the Chosen. Following the destruction of Sunnydale, Giles formed the core of a new Watcher's Council along with Wells, Andrew and Xander Harris.
Considering that there were plans for a Ripper series featuring Giles in England, one assumes that he's has been having adventures of his own during his time in the U.K.