Dogs of War
The mercenaries of the Warhammer Fantasy world. Used to have their own codex and models yet have been sadly discontinued. Comes in three flavors; regular mercs, special characters, and Regiments of Renown.
Regiments of Renown units have their own backstory and special models. This used to be the only way you could get Witch Hunters onto the table before the new Empire army book.
Most mercs come mainly from Tilea which is the Warhammer Fantasy version of Italy during its city state period.
Total War: Warhammer players regularly speculate if they'll appear in that game in some capacity, though aside from when a Creative Assembly mistakenly namedropped them on stream (he was actually referring to the prize including a DLC for Total War: Rome II named Beasts of War), there hasn't been any true indication of it ever happening yet.
Models
Games Workshop still sells some of the regiment of renown models although the prices are worse than Forge World