When we first meet Cordelia she is the epitome of the popular girl. Beautiful and rich, she is the leader of a clique of girls - dubbed the Cordettes - who follow her around hoping that her fabness will rub off. She greets Buffy on her first day at Sunnydale High with a quiz on cool. Although Buffy passes, Cordy later rescinds her membership into the Cordettes when she finds her hanging with "losers" ({{WillowRosenberg}}, {{XanderHarris}} and {{Jesse}}) and running through the Bronze with a wooden stake.
Over time, Cordelia begins to put 2 + 2 together and discovers that Buffy is not in a gang, as she originally suspected, but rather she is fighting the evil that has infested Sunnydale. Cordy decides that she wants to survive and it's best to have Buffy and the Scoobs on her side. Of course spending time with the Slayerettes begins to affect her, first in the form of a smoochie relationship with Xander and later with a little more compassion, tenderness, and respect.
Although like any Whedonverse character she suffers much trauma and humiliation - for example Xander cheats on her with Willow, and her family loses all their money due to "just a little" tax evasion - she pitches in when it's time to fight against the dark forces. Cordy is right there when the entire school, led by the Scooby gang, takes on the Mayor at graduation.
Due to her family's financial woes, Cordy is unable to go on to college. so she settles for the next best thing... being an actress in L.A. Not long after arriving she meets up with {{Angel}} and begins her career as a demon fighting p.i. She also inherits the gift of prophetic (and painful) visions when she kisses {{Doyle}} (another demon fighter) just before his death. She also got an apartment with a ghost, kept up with the Scoobs through Willow and then became a half-demon to make the pain of the visions go away.
Cordelia and Angel also begain to fall in love with each other, but she found out he had sex with Darla who was pregnant, after she staked herself, to bring to baby to life, Cordelia became mother figure for {{Connor}}, but before she could tell Angel she loved him, {{Skip}} arrived and told her she could became a higher power, she accpted and rose into the sky, while Angel was trapped in a box and sunk into the sea by his son Connor who was kidnapped eariler and taken into a hell-like place where he grew up to learn to hate Angel.
After Cordelia came back to earth from being a higher being (as of yet, her sudden & amnesiac return has not been explained). {{Lorne}} came up with the solution to restore her memory with a spell, which back-fired at first causing the whole gang to think they were 17 years old. The spell was fixed and enabled Cordelia to remeber who she was. Cordelia, still shaken up about past events and her memory of being a higher being, opted to live with Connor.
Later on a big bad appeared aka "the beast", who proved very strong and very tough which made him extremely hard to fight. After a spell the beast performed which caused it to be night 24-7 and caused fire to rain from the sky, Cordelia and Connor had sex (much to the horror of Angel). As time went on Cordelia moved back into {{TheHyperion?}} and helped out the gang with the task of fighting the beast. The only problem was that Cordelia was not the Cordelia we thought she was she had infact been body-jacked by the 'baby' she was pregnant with, all the mishaps that had been happeinig such as Angel's soul gone missing were because of the Higher-power which had taken over Cordelia to become fully human on this plane.
Over time the truth came out and Cordelia fled with Connor to give birth to her baby without Angel causing trouble, After baptizing the baby in the blood of a innocent virgin, Cordelia gave birth to Jasmine a Higher-power who had come to earth to help Angel and the Gang to rid the earth of evil. As a result of the violently magical birth, Cordelia fell into a coma.
After months of unconsciousness, Cordelia finally woke up after a painful vision the powers-that-be sent her, foretelling of Angel's death, after warning the Gang and returning to were Angel now works, Cordelia helped Angel and stopped Lindsey from killing Angel. Later on that day Cordelia talks with Angel in his office and tells him why she has returned; to put him back on track of the mission. After telling Angel that the powers-that-be owed her and she has to leave because her life is on a different path they embrace and kiss...the phone rings, it is the hospital, Cordelia passed away in her hospital bed without ever waking up.