King
King is a weapon upgrade in Dying Light.
This weapon upgrade will add +2.1 to Damage, Handling and Durability of a weapon, and is statistically equivalent to the Clicker upgrade. It is the one of the two best upgrades you can find in Dying Light.
Locations to find this upgrade are rare, but can be obtained in very hard locked chests and hard locked lockers, as well as in The Following DLC Military Chests. A free way to obtain this Upgrade is to play the Dying Light Companion App if you have a smartphone or similar device, and send the "loot" collected by your survivors to your character. Freaks of Nature enemies will have a King when their bodies are looted. You can also get it from looting the killer in the Old Town sidequest "Fan Zone".
In the main game in the Old Town location, the weapon upgrade can be found uncommonly in loot spots, which are marked with signs like "24/7 Bar/Grill" and usually have a medium-lockpicking door and a medium chest inside them.
There is a uncommon chance that in the room protected by a medium lockpicking door, there will be a chest similar to the Very-Hard chest found in Old Town, which usually has pouches in it, but can sometimes give King weapon upgrades. Note that the chest you find in the room doesn't need to be lockpicked.
Duffel Bags in old town rooftops protected by 4 or more thugs also have a chance of dropping King upgrade.
Demolishers found in The Following also have a small chance of dropping a King upgrade.