Gunter

Gunter requires the Breaking Dead DLC.

Gunter is a zombie who was created by the previous graveyard keeper to help with chores. However, he turned to be too smart and got chained to the wall permanently. He will teach you how to create zombies to help you around. He can be found in one of the chambers of the cellar past the dungeon entrance.

Open the gate
In order to be able to access Gunter, you need to examine the zombie work areas such as the large tree or Iron ore mine. Then, next time a body is delivered, and you enter the morgue, a dialog will trigger with Gerry and he will tell you about this chained up zombie you need to check out (NOTE TO CONSOLE USERS; this requires the Breaking Dead DLC). Also requires that the gate behind Snake is open. Once you go to Gunter, another event will trigger where you need to open the gate by pulling a lever.

Some have reported problems with triggering the dialogue with Gerry in the morgue. Introducing yourself to certain NPCs, or having progressed a certain amount of days, in game, might be unknown additional triggers for this dialogue to become available.

He needs to feel pain
Once you're inside his cell, he will ask you to hit him with a sword because he hasn't felt anything in a long time. He's not willing to talk before you do this.

 Warning: Here comes a spoiler! Even though Gerry warns you not to ever set him free, he will remain chained no matter what when you're given the choice to free him. If you try to free him, he will say he's quite content in that cell and that his flesh is too rotten to do anything anyway.

Making zombies
Gunter will tell you to go recover one of his "brothers" north of your home, also teaches you about zombie juice. Examining the broken cabinet near him unlocks some of the zombie-related technologies. To discover the rest of the blueprints, dig up the zombie in the rubble at the passage from the apiary to the forest near the river.

Visit the zombies page for more detailed guide on those willing co-workers.
 * Implemented on xbox, May '19.