Black mask is just the latest black mask among a long line. He at one point was a cop working to clean up the streats that black mask had full of thugs and whores. But like he was experiencing now the old black mask had gotten old and tired of the visage.
So black mask kidnapped him since he was the shining ray of hope for the city and just every black mask since the begining he had to falter and turn.
Black mask grabbed him outside of police headquaters after his shift and when he woke up he was in what could only be described as a jail cell without the amenities. He had no idea why he was there or what was going to happen to him all he knew was it wasn't
going to be good.
When black mask walked in he carried with him another mask just like his. It was at this point that the cop realized what was going on he was going to be forced into black mask's group.
Black mask askes him on time if he would like to willingly wear the mask and become his replacement in a few months. To this he spat back that he would rather die than join black mask.
It was at this time that black mask nodded to his helpers to restrain him that he realized there was no choice he was going to be forced into wearing the mask. After the mask is applied he is let go and he instantly tries to remove the mask from his head
only to discover that it has become his head.
(shoot ahead a few months)
At this point the mask has taken over his body and turned what at one point was the shining ray of hope for gotham into its worst enemy.