Black Mask (Arkhamverse)

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

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
As Bruce Wayne entered Arkham City, Black Mask was seen as one of the criminals being transferred. Sionis was seen fending off the TYGER forces with a chair, and eventually detained by the guards.

With Black Mask indisposed, Sionis Industries became the Joker's lair in Arkham City.

Black Mask took advantage of the turf wars, and procured a lair by allying himself with the Riddler. Robin infiltrated the hideout and took down Black Mask's men while Sionis himself escaped. While Batman was preoccupied, attempted to mount an escape from the city aboard a freight train, where he was aided by stray thugs one of the Abramovici twins. Fortunatley, Sionis was stopped by the Boy Wonder before he could escape.

Psychological Profile (by Dr. Young)
Black Mask

Real Name: Roman Sionis

CANDIDATE FOR ADVANCE RESEARCH?

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.