A battle droid (also referred to as war droid, combat droid, or killer droid) was any droid designed for combat.
There were numerous types of battle droids. They predated the Galactic Republic by thousands of years, with the earliest known being Rakatan guardian droids and the war-robots used by Xim the Despot. Many of the best known battle droids were those used by the Confederacy of Independent Systems during the Clone Wars. At the end of the Clone Wars, Sith Lord Darth Vader turned off the Master control signal, deactivating most of the Separatist Droid Army. After this, battle droids were extremely rare. One thing all battle droids had in common was that they had limited intelligence. They were programmed to follow orders, and not much else, though they did have personalities.
In the Kingdom Hearts Unlimited Saga, Battle Droids are common enemies found across the worlds under the command of the Separatists, alongside the far more deadlier Wraithlings, during the events of "Birth of A New Era". They are all destroyed by the newly created Darth Vader upon his forging between that of the soul of Darth Sidious and the blank clone of Anakin Skywalker. Eventually, the Droids are re-activated by Sidious upon his return and soon make up one-sixteenth of the massive Grand Imperial Army under Vader, Governor Tarkin, and General Grievous' command.