The young woman who came to be called Darla was a prostitute in the Virginia Colony. In 1609, she was sired on her deathbed by the Master, the self-proclaimed lord of the vampires and leader of the clan of vampires known as the Order of Aurelius. In a short period of time, Darla became a creatively scheming, not to mention deadly vampire in her own right, and also became the Master’s personal favorite.
Masquerading as an Irish noblewoman in Galway, Ireland in 1753, Darla transformed Liam into Angelus, the Scourge of Europe, training him, teaching him, and loving him for over 150 years. The two spent every deliciously bloody moment together, leaving a trail of death and destruction in their wake. Darla and Angelus even created their own special little family of vampires throughout the centuries, first with James and Elizabeth, an undead Romeo and Juliet. The two gained the most notoriety when they paired with the deadliest members of their bloodline, Drusilla and Spike, in the latter half of the 19th century.
In 1898, fate came in the form of a beautiful gypsy girl, just one of Darla’s many inventive and carefully thought out gifts for her beloved Angelus. Little did Darla know that as a result of her gift, the girl’s family would restore Angelus’ soul. As a result, Darla rejected Angelus when his soul was returned — just when he needed her the most — throwing him out into the streets of Romania to fend for himself. Angelus unsuccessfully tried to get back in Darla’s good graces over the next two years. During the Boxer Rebellion in China in 1900, he refused to kill a baby Darla kidnapped for him. They would never meet again until nearly 100 years later.
Parting ways with Drusilla and Spike, Darla rejoined the Master’s Order of Aurelius. She arrived in Sunnydale, California in 1997, in an attempt to free her sire from the Hellmouth. At the same time, Angelus — now called Angel — also was in Sunnydale and in love with Buffy Summers the Vampire Slayer. Failing to bring him back into the fold, Darla attempted to trick Buffy into believing Angel fed off her mother, when in reality, she did. Her plan failed miserably, however, and Darla was killed by Angel’s hand.
The Scrolls of Aberjian had a different future in mind for Darla, who was resurrected as a human by Wolfram & Hart in Los Angeles, California, in 2000. She was the first vampire to be a born-again human, a stark contrast to Angel, a human in the body of a vampire. The memories of Darla’s past, now tempered with a conscience, began to eat away at her. To make matters worse, she was dying of syphilis. Despite his best efforts to cure her, Angel failed; nonetheless, the human Darla was grateful. Before they could explore any other options, Drusillla returned and ushered Darla once again into the darkness.
Darla and Drusilla went on a killing spree in LA, betraying — and eventually slaughtering — a number of Wolfram & Hart lawyers. Angel broke up their alliance after setting them on fire. That didn’t stop Darla from tormenting him. In the throes of despair, Angel had sex with Darla in the hopes of losing his soul. When he didn’t in the aftermath, he told Darla to leave his city or else he’d kill her if he saw her again.
The night they copulated had unforeseen consequences: Darla was pregnant, despite the fact vampires cannot reproduce. The unborn baby was protected by a higher power, therefore making Darla unable to kill it. She returned to LA seeking Angel’s help. They learned the baby was part of a prophecy stated in the Nyazian scrolls. It was also revealed that the unborn child was a boy — a human boy with a soul.
However, since Darla was incapable of delivering a baby, the child was dying. Repenting her sins, Darla told Angel that this child was the one good thing they ever did together. In a selfless act, she staked herself, freeing the baby from her womb, leaving Angel to raise their son alone.

source:  City of Angel