hired gun
US /ˈhaɪərd ˌɡʌn/
UK /ˈhaɪərd ˌɡʌn/
1.
a person whose services can be bought, especially a mercenary or assassin
:
•
The company brought in a hired gun to deal with their legal troubles.
•
He was known as a hired gun, always ready to take on dangerous assignments for a price.