noun
slave-driver manager; heartless section chief
Colloquial, often half-joking term for a strict, demanding, or unsympathetic boss. The 鬼 (oni) prefix intensifies the harshness.
うちの鬼課長は、残業を断るとすぐに怒る。
Our slave-driver manager gets angry the moment you refuse overtime.
新入社員はみんな、あの鬼課長にびびっている。
All the new employees are scared of that heartless section chief.
鬼軍曹 means 'drill sergeant' or 'stern sergeant' and is used in military contexts, whereas 鬼課長 is for a corporate manager.
Compound of 鬼 (oni, 'demon') and 課長 (kachō, 'section chief'). The prefix 鬼- is used figuratively to mean 'fierce' or 'heartless'.