IMO. Roman Sionis owner of his company that almost rivals Wayne Enterprises. Sionis is a corrupt businessman,who would kill someone rather than asking to move aside. He has everything,but is jealous of his rival Bruce Wayne,but keeps acts all friendly towards him. When his proposal to merge his company with WE falls through,Sionis resorts to hiring gangsters to sabotage WE property and using Deadshot to kill the board of directors. With the company in ruin,he will cease the chance to take it. Roman becomes Black Mask in order to divert any suspicion or attention away from himself,by making up a false story that Thomas Wayne murdered his parents and is out for revenge by destroying his son. This of course is to deliberately sabotage Bruces creation of The Thomas And Martha Foundation.
Batman and Black Mask both draw the attention of a certain feline woman in the process,but why?