"Tact is just not saying true stuff, I'll pass"
Cordelia Chase. May Queen, leader of the most popular group in school, what Cordy says, goes. Daughter of one of the wealthiest men in Sunnydale, Cordelia grew up to regard herself as the center of the known universe and everyone else revolves around her ("Well revolve out of my light!")
This wilfully narcissistic view didn't make her many friends in the lower circles of school, and created a monster: The We Hate Cordelia Chase Hate Club (Treasurer, Xander Harris)
When new girl from LA, Buffy Summers, started at Sunnydale High, Cordelia tried to befriend her, but cut her loose when she saw her getting friendly woth the 'lower elements of the school' (Xander, Willow and Jesse) and nearly getting staked by Buffy didn't help either.
Cordelia stayed out of their way until people around her started getting hurt; her then-boyfriend was beaten up in the locker room and her best friend Harmony was pushed down a flight of stairs. Cordelia came to Buffy for help. Buffy tracked down the invisible girl that was plaguing Cordy's life and saved her from getting a free face-job of said invisible girl.
Slowly, Cordy started to get integrated into the Scooby Gang, saving Willow and Jenny Calendar from a horde of vampires when the Master rose.
Cordelia took the weirdness in her stride and started to become an (occassionally) essential part of the Slayerettes, giving lifts, doing research ("Wow, they have a dmeon for everything.") and even getting her hands dirty and fighting.
She also found love in the Slayerettes in the form of Xander Harris, a boy she considered to be a total loser. This being said, she tried her hardest to hide her attraction to him from the rest of the school by carrying out their affair in a number of broom closests. But word still got out and facing huge amounts of ridicule, decided to dump Xander on Valentine's Day which led him to cast a love spell on her (that went badly wrong). When she realised what he had done for her she decided that "she wasn't a sheep" and could date whoever she liked "even if he was a total loser".
Unfortunately, love didn't run smoothly for Cordy. Xander fell in love with his best friend Willow and found them kissing when she and Oz (Willow's boyfriend) came to save them. A little distraught, she ran off, falling through a weakened stairway and impaling herself on a metal pipe.
After dumping Xander (and once again being the ridicule of the whole school) Cordelia met Anya, a the Patron Saint of Scorned Women (disguised as a twelfth grader, who told her to make a wish. Cordy wished that Buffy (the bane of her life) had never come to Sunnydale.
The wish was granted and Sunnydale changed. No longer a fairly safe place to live it was ruled by vampires, there was a curfew and the school was nearly deserted (because so many of the students had either been killed or changed).
Wandering the streets of the alternate-Sunnydale Cordelia ran into Xander and Willow, now vampires. They tried to attack her but she was saved by the 'White Hats' (This reality's version of the Slayerettes, Giles, Oz and Larry) She tried to explain to them that Buffy needed to come to Sunnydale to stop the Master, but unfortunately before Buffy came to town Xander and Willow caught up with her and killed her.
Giles believed Cordelia's insane story about another reality and everything being different and found Anya's magic talisman and smashed it, breaking the wish and returning everything back to normal.
However, things didn't get better for Cordelia. Lonely in amongst the popular group and seperated from the Slayerettes she thought life couldn't get any worse. This being Sunnydale it did. Her father had been making a mistake on his taxes (for twelve years) and the IRS found out. Now her family was penniless, and Queen C has to get a part time job to pay for her own Prom dress.
Things did look up for a while with the arrival of Faith's new Watcher, Wesley, but after discovering he was a terrible kisser Cordelia decided to leave him well alone.
The Ascension came, and went. Cordelia graduated, managed to survive High School (although the school didn't survive them). There was nothing left in Sunnydale for her, it was time to make a new start...