The King of the droids ploy was an espionage tactic used by Wraith Squadron.
The tactic involved using one or several droids to subvert other, simpler, droids - mostly house-keeping and maintenance ones - to do what the controller wants them to, such as report on enemy movements or sabotage enemy machinery.
Gara Petothel first used this tactic when she was on Warlord Zsinj's flagship, the Iron Fist, using her R2 astromech droid to capture and convert MSE-6 mouse droids on the ship, so they could disable the ship's hyperdrive to trap Zsinj when he was confronted by New Republic forces.
In 44 ABY, Trey Courser of the new Wraiths investigating General Stavin Thaal, developed a similar tactic without knowing Petothel's. They used this tactic to infiltrate Borsk Fey'lya Army Base on Vandor-3 by disguising the droids as blaster cartridges. In order to speed things up, the Wraiths attacked the base's patrols and confiscated their weapons under the guise of the Quad-Linked Militant Pacifists a fictional terror group created for that purpose. This required new requisition orders for weapons which meant that the Wraith-modified weapons were issued to the patrols.