Charisma Carpenter as Cordelia Chase

Next to Willow, Cordelia is probably the character who has evolved the most over the last two seasons. She has gone from vapid and snobby to a self-centred but reliable friend to the Slayer and Slayerettes. She has begun to let down her guard, and has become a much more likeable character.

Cordelia has evolved throughout the first two seasons of the show from a snobby, vapid airhead who was a nemesis to the Slayer and Slayerettes, to being very much one of the gang. Not only did she start a relationship with Xander (although they still bicker all the time), but she is becoming a good friend to Buffy and Willow. Cordelia is one of the most popular girls at Sunnydale High School, a cheerleader and homecoming queen.

Episodes Featuring Cordelia
Cordelia is a regular character, and as such is in every episode. Listed below are episodes which feature his character specifically, or in which significant character development occurs.
(All transcripts generously provided by AleXander)

Season One
2. Out of Mind, Out of Sight: Cordelia becomes a symbol of all the popular people at Sunnydale to an unimaginably ignored girl.

Season Two
1. Reptile Boy: Cordelia and Buffy attend a frat party at the local college, but they meet more than just older guys.
2. Bewitched, Bothered & Bewildered: Xander and Cordelia's relationship becomes public knowledge, which threatens her status as a popular girl. She uses Valentine's day as an opportunity to break up wit him, but he is not happy about it. His plan to get her back backfires however, and she ends up being the only woman in Sunnydale who isn't obsessed with him as the two fight for their lives.