The ID Reaper refers to the specialist:
The product of a cutting-edge military R&D project to supplement Special Operations soldiers in the field, Experimental War Robot-115 was one of a single unit of advanced prototype combat robots running the most sophisticated AI software ever seen.
After several politically embarrassing mishaps and budget overruns, the project was cancelled and most of the prototypes were stripped for parts.
Fate had other plans for EWR-115, when years later it was discovered to have been stolen.
Reports of sightings of the terrible machine on battlefields around the world began to surface. No one knows why it fights or who, if anyone, is issuing its orders.
- Experimental War Robot-115 "Reaper" - callofduty.fandom.com