My story is set in a medieval fantasy setting.
The Empire has the ability to create "Soulless". These are able bodied men and women who have been stripped of their free will and personality. In essence, they are meat automatons. After the process is finished, a soulless will only take orders from specific imperial commanders , known as emissaries, unless told otherwise. One needn't give them explicit orders. They are capable of understanding the meaning of more vague orders like, "Attack", "Bring him here", etc.
Soulless will follow orders without a moment's hesitation. While they have enough self preservation instincts to protect themselves or to avoid obvious obstacles, but this can be overridden by a command, such as: "Walk into that burning building" or "Stab yourself with a rusty spoon".
They do not , or at least do not seem to, experience pain. A soulless will never show emotion. You can systematically shatter its bones or attempt long term psychological torture, but it will not react.
There are a few drawbacks. Soulless lack initiative. Once they have completed their order, they will return to their commanded for further orders. For instance, they will fight in a battle, but will not pursue fleeing enemies, but won't pursue do to them being a non threat. They are by all accounts, still human. They need to be cared for like any pet (food, water, sleep, occasional cuddles, etc.). They will push themselves until their bodies give in, so attrition is a valid tactic. Just like humans, they posses squishy organs, whose absence result in death.
I intend for the soulless to be a very real and very scary threat. Something that even a seasoned veteran is afraid to fight. So, would the soulless prove to be a much greater threat than a standard enemy?