Black Mask (Arkhamverse)

Black Mask is referenced in Batman: Arkham Asylum and appears in Batman: Arkham City.

Road to Arkham
According to Oracle in the Road to Arkham prequel oneshot, Black Mask was involved in a gang war and retreated to Bludhaven, home of Nightwing.

Batman: Arkham Asylum
While Black Mask does not appear in Batman: Arkham Asylum, his original wooden mask is mounted on the wall of Dr. Young’s office in the old Arkham Mansion. A newspaper clipping about Roman Sionis before he became Black Mask also appears on a bathroom cabinet in the Patient Observation room of Arkham Asylum's Medical Facility. Black Mask is referenced in the game in many of the Penitentiary cells, for example, in the cells is a drawing about a little boy and a house on fire, and then the devil rises up and takes the remains, and the boy is happy.

Batman: Arkham City
It's been revealed that Black Mask was the only inmate to ever escape Arkham City, doing so using explosives he stole from Penguin to blow a hole into the perimeter wall. This prompted Strange to line the wall with automatic machine guns that would instantly kill anyone who approached.

As Bruce Wayne was being admitted to Arkham City, Black Mask was seen as one of the criminals being transferred into the cell block, having finally been recaptured by Tyger Forces. Sionis was busy fending off the TYGER forces with a chair; however, he was eventually detained. Using this to his advantage, the Joker was able to capture Sionis Industries and it was quickly modified into Joker's Funland, Joker's base of operations in Arkham City.

With the growing violence in Arkham City, as the three primary gangs (Joker's, Penguin's and Two-Face's gangs) fighting for control over the city, Black Mask secretly allied himself with the Riddler and slowly built up his forces for his plans to retake Arkham City in the confusion.

Challenge Maps
As the Dark Knight was preoccupied with his investigation into Protocol 10, Robin infiltrated Arkham City to investigate Black Mask's activities. After some work, Robin was able to determine the location of Black Mask's hideout and set out to take down Sionis. Robin fought against Black Mask's forces giving him time to escape from Robin aboard a freight train. While in pursuit of him, Robin was forced to fight his way through stray thugs belonging to the various gangs and Mister Hammer of the Abramovici Twins.

In time Robin was able to locate Black Mask and took him into custody.

Psychological Profile (by Dr. Young)
Black Mask

Real Name: Roman Sionis

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Psychological Profile: A mild psychopath, Sionis has narcissistic tendencies but the main malady he suffers from is resentful obsession with, of all people, billionaire Bruce Wayne. Sionis is fixated on Wayne possibly due to childhood traumas that he has projected onto the idle playboy. It is difficult to say whether the two actually knew each other as children, or if this is Sionis's invention. However, it is Sionis's criminal activities, and the role playing that resulted in the black skull-like mask accidentally burnt into his skin, that resulted in his committal to Arkham.

Additional Notes

I'd question whether Sionis is actually insane, if not for the choice of his obsession; I can't imagine being interested in (much less stalking) such a pointless personage as Bruce Wayne.

Trivia

 * When Bruce Wayne sees Black Mask when entering Arkham City, it is likely that this is Black Mask's second time entering Arkham City, as Black Mask was the first and only inmate to ever escape, as revealed by a riddle that unlocks an Arkham City Story. Therefore, the Robin DLC is most likely a second escape attempt.
 * The Penguin may have Sionis's first mask or a replica in his Iceberg Lounge, indicating that Black Mask may at one point have been his main rival.
 * Black Mask's forces are oddly absent during the events of Batman: Arkham City, likely because Sionis was re-entering Arkham City during the game and had no thugs under his control.
 * The small part of his mask that is broken shows an undamaged forehead and some hair, suggesting that either his face had healed at some point or his mask is actually removable.

Game Over lines
thumb|300px|right|Black Mask's game over screens.
 * "First you fall, then Gotham."
 * "What? Did you think you could beat me? Me?!"
 * "No one goes up against the Black Mask and lives."