Raiders are human enemies who drop items such as the shotgun. Their purpose is to scavenge from houses and kill everyone in their way.
The second non-player character that the player may encounter is a raider who appears at the finish of the tutorial if the stove fire is not started. He enters your house first through the front door. If you get in his way, he will try to kill you, but if you don't, he walks up to Kates room. He will say "Howdy Neighbor" once he opens the door to her bedroom, to which she responds "What the h*** are you doing here?" It's at this point that you are supposed to quietly emerge from another room and kill him with your hammer. If you alert him early, he will kill you with his shotgun. If you do not approach him and kill him, he will shoot Kate. When killed, he yields a shotgun, a baseball bat, a lighter, and 36 shotgun shells.
There is a second raider in the Tech Demo which can be found in a supermarket to the southeast. when approached he will warn you to leave the shop and if you dont he will kill you.
You can kill the second raider by opening the first door, then walking to the second door and entering. The raider will be focused on the previous door, so as long as you dont walk in his line of sight. He drops a lot of loot.