Rupert Giles was assigned to be
Buffys watcher when she arrived in
Sunnydale.

Their first meeting in the library was a
shock to Buffy and when confronted
with a book titled 'VAMPYR' she bolted.

Giles has always been the adult voice of
reason within the group and was even
accused of having too much of a father's love for
Buffy after telling her of a council test.
For that reason he was fired from the
council of watchers only to be reinstated recently.

Giles moved back to England when Buffy died,
and returned for a short time when he learned that
she had been brought back by Willow.

Willows addiction to the Magic's almost cost Giles his life
when he came back after hearing a powerful force had
risen in Sunnydale.
Luckily Xander managed to touch the last shred of humanity in Willow and therfore saving Giles, and the world.