What does "hatchet man" mean?

A person assigned or hired to carry out a disagreeable task or unscrupulous order. For example, When it came to firing an employee, Arthur was his boss's hatchet man. This expression originally referred to a hired assassin but in the mid-1900s was transferred to less nefarious enterprises.

A person who attacks the reputation of others, especially a journalist hired to do so, as in You can count on Mary's column to destroy the mayor—she's the perfect hatchet man. This usage gave rise to hatchet job, meaning “harsh destructive criticism.” [Mid-1900s]