Darla

This 400-year old vampire was turned by the Master. She remained by his side for many years until she met Liam - a young never do well, that she turned into Angelus. When she loses him she returns to her sire and heads over to Sunnydale, where she encounters Angel again. Plotting to turn him evil again, she attacks Buffy but Angel turns on ehr and stakes her.
Brought back to life - human - by Wolfram & Hart, she torments Angel.When she finds out she is dying of syphillis - illness that should have killed her hundreds of years ago, she desperatly tries to get turned. She finally accepts her fate as a human when Drusilla vamps her once more.
She still tries to get Angel back and eventually leaves, realising she can't make him lose his soul. She reappears in L.A., pregnant - by Angel's sin - and stakes herself to give birth to her child, Connor.