Television. Wesley is introduced in the Buffy the Vampire Slayer season three (1998–1999) episode "Bad Girls" as the new Watcher of Buffy (Sarah Michelle Gellar) and Faith (Eliza Dushku).

Why does Buffy get a new Watcher?

Watcher to Buffy and Faith

Wesley was sent to Sunnydale by the Watchers Council to serve as a replacement Watcher for both Faith Lehane and Buffy Summers, after Rupert Giles had been fired. ... Wesley's mistake only earned him further disdain from Buffy and her companions. Wesley joins the Graduation Day battle.

Why did Giles stop being Buffy's Watcher?

He left Buffy for a while in season five, which aired in the year 2000, having realised Buffy no longer needed him. He only appeared in the following episodes as a guest. Head said the reason he had left the series was so he could spend more time with his family, who still lived in the UK.