Rupert Giles attended college in Oxford where he fell into dubious company, and began practising in the black arts. He then followed the family tradition and became a Watcher.

Before being sent to Sunnydale to supervise Buffy's training, Giles worked in "a British museum". His job as the school librarian affords plenty of opportunity to immerse himself in ancient tomes of prophecy, unravelling the obscure riddles which might help protect his protégé.

Giles was assigned to Buffy when her previous Watcher was killed, and she was forced to relocate. Although they have a quirky relationship, their loyalty and respect for each other is obvious.

Now he is a man of leisure, as Buffy no longer works for the council, he's not a Watcher, and as Buffy no longer goes to school, he's not a librarian.

But they all still need him though.