taskmaster

noun

1. Someone who supervises workers, especially one who imposes hard or burdensome work.

   “And the Lord said, I have surely seen the affliction of my people which are in Egypt, and have heard their cry by reason of their taskmasters; for I know their sorrows”

2. (figuratively)A source of hard work or responsibility.

   “It all looked so easy when the competent were at the helm, but reality is a cruel taskmaster, and all the excuses that worked as an underling wear thin once the incompetent are in leadership roles.”