Someone who has been persuaded by an offer of money to do an unpleasant or unpopular job. (Cambridge Dictionary)
A person who serves for hire especially for purely mercenary motives. (Merriam – Webster)
If you refer to someone as a hireling, you disapprove of them because they do not care who they work for and they are willing to do illegal or immoral things as long as they are paid. (Collins Dictionary)
A person employed to do menial work. (Oxford Dictionaries)
A person who works purely for material reward. (Oxford Dictionaries)
Hireling and Underling. Thesaurus. Plus.
Are you an under shepherd or a hireling?