1) Coercer 2) Extorter 3) Extortioner 4) Extortionist 1) Criminal 2) Criminal with dirt on someone 3) Crook 4) Extortioner 5) Extortionist 6) Felon 7) Malefactor 8) Outlaw 
• (n.) One who extorts, or endeavors to extort, money, by black mailing.
Black'mail`er noun One who extorts, or endeavors to extort, money, by black mailing. 
[n] - a criminal who extorts money from someone by threatening to expose embarrassing information about them
extortioner noun a criminal who extorts money from someone by threatening to expose embarrassing information about them