Karl in his many forms
Karl is a cop that always appears in escape mode when you need to enter doors. Either him or another normal guard will open the door for you. He can be identified because no matter what, he does not wear body armour or carry tasers. He doesn’t appear anywhere else and cannot be killed. The nametag: Karl can be seen under him. He can never get tired and can never die. He never attacks prisoners.
In console edition Karl will also escort you to the infirmary if you’re unconscious and your cell/solitary if in lockdown or solitary if no guard is sent for a while. He also gets tired and will go to the staff room, potentially forcing you to wait as he takes his break with you handcuffed, though you will not be attacked for being in a off-limit area while escorted. Karl can be killed and has low health, and also neither catches you misbehaving or will alert guards if you attack him.