She is portrayed by Julie Benz.
Darla was born in late 16th century Britain. She emigrated to Virginia Colony in North America where she became a prostitute. She was dying of syphilis when The Master changed her into a vampire. Darla quickly became one of his favorite henchmen and he viewed her like a daughter. Over the years she killed many innocent people for fun before being intrigued by a boy named Liam. She sired him and he became the infamous Angelus. At her urging, Angelus murdered his family and everyone else in his village.
The two of became infamous together with Darla leaving The Master for now. Together they killed Daniel Holtz's family because he was a famous vampire hunter. Darla and Angelus were joined by Spike and Drusilla becoming known as The Whirlwind. Darla brought Angelus a gypsy girl to feed on. This led them to curse Angelus with a soul. Darla noticed his odd behavior and figured it out causing her to abandon him.
She rejoined The Master and assisted with his plans in Sunnydale before running into the ensouled Angel who killed her after she attacked Buffy's mother. Wolfram and Hart resurrected her a few years later to turn Angel back to his dark side. Angel encounters her and she claims to be someone else. It turns out that she was revived as a human and she now has a soul. The plan failed and they had Drusilla turn her back into a vampire. Darla and Drusilla went on a rampage across Los Angeles and attempted to attack Angel but failed. The two of them left with Darla returning and sleeping with him in an attempt to turn him evil again.
Darla discovered that she was pregnant and sought out help for this to figure out why. No one was able to tell her how it occurred so she returned to Los Angeles and told Angel what was going on. Darla shared a soul with her child prompting her to attack an innocent boy so she could share the blood with her unborn son. Darla appeared to be having difficulties giving birth and her son would most likely not survive. Plus Daniel Holtz who had been put into suspended animation and awakened was seeking to take the child for himself. With this Darla staked herself in order to make sure her son survived. Darla turned to dust but her son survived.
Darla visited her son Connor when he was under the influence of Jasmine (who had possessed Cordelia) begging him not to help her kill an innocent girl. Connor ignored his mother when Jasmine told her that she was lying to him. He then dragged the girl to Jasmine and killed her. Darla then vanished after that because she had been unable to stop her son from helping Jasmine.
Buffy The Vampire Slayer Big Bads