When you arrive on a planet upon deployment, you will be immersed in the depths of unknown territory where threats will be unavoidable. Some of those threats will be Hostile Agents (NPCs).
The kind of Hostile Agent you will encounter may vary based on the location, but you can encounter Workers, Troops, Drones, Turrets and Militia forces.
Hostile Agents will usually guard important sites and valuable loot, patrol around the map and prevent you from easily acquiring resources.
Upwell: Workers and Guard
Militia Scout, Ghost, Breacher, Raider
Drones
Turrets