The Orphan was the personal assassin and enforcer of the human trafficker known as "Mother".
Orphan (David Cain)
David Cain was "acquired" by Mother as a child to serve as her personal assassin and enforcer when she first started her human trafficking network.
Garbed in white, Cain possessed a gas mask that fed him a variant of Professor Jonathan Crane's Fear Gas to keep him on a physical and mental edge (although the dosage is not enough to render him catatonic).
After noting flaws in David Cain, Mother secretly began training new Orphans to serve as a private army and one day replace Cain as her enforcer.
On the apex of her plan to hypnotize the world's children to be her agents, Mother killed David Cain and sent her Orphans to defend her antenna relays around the world from the Bat Family and their associates.
Orphan (Cassandra Cain)
After she was taken in by Batman, after Richard Grayson defeated Mother's human trafficking network, Cassandra took on the "Orphan" title previously carried by her father as part of her costumed persona while patrolling Gotham City.