slave-driver

/S L EY1 V D R AY1 V ER0/
noun
  1. 1

    An overseer of slaves at work; a person who puts slaves to work.

  2. 2

    An employer who demands excessive amounts of work from employees.

    โ€œHe's such a slave-driver! I can't believe he wants us to come in on Saturday.โ€

Source: https://en.wiktionary.org/wiki/slave-driver