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Name: "The Mad Dog" Cain
Identity Status: Public
Maritual Status: Unknown
Last Known Residence: League of Assassins Lair
When he learned of the theories David Cain was developing to train a perfect killer, Ra's al Ghul supplied Cain with infant test subjects in the hopes of creating a new generation of assassins. This experiment proved disastrous; those infants that survived eventually turned on one another until only one boy remained. Ra's ordered one of his "Ubu" guards to kill the boy "like a mad dog". The guard, however, took pity on the abused child, and secretly set him free in the woods. Cain and Ra's al Ghul did not know that the boy still lived, and Cain began a new experiment, raising his own daughter, Cassandra, to replace his earlier failures.
Ra's al Ghul's daughter, Nyssa Raatko, did know that "The Mad Dog" had survived. Years later, after Ra's' death, she sought out The Mad Dog and made him a member of her new League of Assassins. She took him on as a protegé, telling him everything about the experiments, and about who he was intended to be.
Years later, Cassandra had gathered evidence indicating that Lady Shiva was her mother, and sought out Shiva to confirm this. At the time Shiva was the sensei of Nyssa's new League. When Batgirl arrived she caused a series of events that resulted in the destruction of Nyssa's stronghold and the fragmentation of the new League. The Mad Dog went on a killing spree, killing the League members before confronting Cassandra herself, calling her his "sister".
The Mad Dog was successful in killing Batgirl, who gave her life to protect the last of the defected assassins. Cassandra was quickly restored to life in a Lazarus Pit by Shiva.