Complex sentence: Riddick is pursued much of the story by Toombs and his Mercis short for mercenary-who mercenary/bounty hunters, such as show in Pitch Black with the bounty hunter named William J. Johns, Cole Hauser.
Split into simpler sentences: Riddick is pursued much of the story by Toombs and his Mercs. Merc is short for mercenary-who are mercenarys/bounty hunters, such as shown in Pitch Black with the bounty hunter William J. Johns, Cole Hauser.