He's a 'fiend' for physical fitness. [=he is very devoted to physical fitness]
She's been working 'like a fiend'. [=working very hard]
a dope/drug 'fiend' [='addict']
(..) No. We're lost. This is a sanctuary. Please, Christabella, they lured my Anna. They gave her to the fiend. Eleanor, you must remember that Anna went against our laws. She went alone outside into the devil's playground. She was not the responsibility (..)2006 Silent Hill