slave driver

noun

1. an overseer of enslaved laborers and enforcer of hierarchy and discipline in the institution of chattel slavery.
2. a hard taskmaster:

   His boss was a slave driver.

slave-driver

noun

1. (esp formerly) a person forcing slaves to work
2. an employer who demands excessively hard work from his employees

Word History and Origins

Origin of slave driver¹

An Americanism dating back to 1800–10