What is the name of the chaos mage who is a former friend of Giles?

The chaos mage who is a former friend of Giles is Ethan Rayne. Ethan was part of Rupert Giles’s rebellious occult past, when Giles was known by the nickname “Ripper” and experimented with dark magic.

As young men, Giles and Ethan studied magic together and became involved with a group of occultists. Their friendship collapsed after a dangerous encounter with the demon Eyghon, which resulted in the death of their friend Randall. Giles eventually turned away from that lifestyle, but Ethan embraced chaos and became a recurring troublemaker in Sunnydale.

Ethan’s most memorable scheme occurs in “Halloween,” when he enchants costumes sold at his shop. Anyone wearing one becomes the identity represented by the costume, causing Buffy and the other students to lose their normal personalities. In “The Dark Age,” his connection to Giles’s past becomes central to the story, while “A New Man” turns Giles into a Fyarl demon.

Willy is a bartender and informant, D’Hoffryn leads the vengeance demons, and Rack is a dangerous warlock associated with Willow’s addiction to dark magic. None is Giles’s former chaos-worshipping friend.