The film
Super-soldier recruit Tsui Chik is forced to escape with his comrades after the project is canceled. Months later, he's trying to have a quiet life as a librarian with his best friend, Inspector Shek Wai-Ho. However, a string of vicious gangland murders begins that has all the markings of Tsui's former compatriots who seem to have turned to crime. Realizing that the police are helpless, he decides to take them on himself. With a disguise, Tsui becomes the mysterious superhero known only as Black Mask.
Synopsis from TMDB.
The name
Also in Black Mask