After the creation and failure of the Paradise Matrix, The Architect created the Nightmare Matrix and based the design of that Matrix beta on human beings' perception and violence towards one another, the reason for why the first Matrix was a failure. Within the Nightmare Matrix, The Architect created supernatural monsters to fit the environment and situations for bluepills.
Abel, along with fellow vampire program Cain and phantom programs of The Twins, were created and situated within the Nightmare Matrix. After realizing that the Nightmare Matrix was another failed Matrix beta, The Architect rebooted the system and deleted all existing programs created for the Matrix.
However, before Cain, Abel, and other programs were deleted, The Merovingian protected all of the programs he thought will be of good use for him and saved them from deletion. Upon rescuing, the surviving programs started to work for The Merovingian in helping him and his wife Persephone as they also knew their kill-code, as threat from their existence.
Serving The Merovingian
During the near end of the Machine War, all Machines and programs realized that the Resistance was close to winning the war with the help of The Oracle. To prevent The One from reaching the Source, The Merovingian captured The Keymaker and locked him in his Chateau to not have any members of the Resistance to locate him.
Together with his partner Cain, Abel intentionally let The Keymaker escape from his prison beneath the Chateau to steal the key meant for The One outside of The Merovingian's circle of influence.
But Abel foiled the plan by telling The Merovingian about the betrayal. Eventually, the key was destroyed by The Merovingian, forcing The Keymaker to create another one.
When Persephone led Morpheus, Trinity and Neo to The Keymaker's cell, she shot him in the head with a silver bullet, demonstrating the special method of killing a werewolf program and allowing the Resistance to retrieve The Keymaker.