KLR-B1, or Killer as he was eventually known as, was the first prototype KLR series combat droid created during the Clone Wars. During the initial system trials, the technicians discovered flaws in the KLR series' software programming which had allowed them to bypass their failsafes. Though they attempted to shut down all four of the droids, KLR-B1 managed to escape this process and proceeded to kill all base personnel shortly after the Separatist attack on Tembora. Since this time, small starships periodically crashed on the rogue planetoid and any surviving crewmembers who made it to the Tembora Research Station were swiftly killed by KLR-B1. At first he killed them swiftly, but soon learned that toying with them and drawing out their deaths was much more satisfying.
When members of the Maid of Sentiile sent a recon group to the base and discovered that it was abandoned, the full crew of the ship proceeded to enter the base. It was not until some members had already managed to load KLR-B2, KLR-B3, and KLR-B4 onto their transport that KLR-B1 attacked and killed the entire recon team. Some of the other crew members managed to escape with the three other prototypes, and KLR-B1 kept Gillon alive to torture him with a portable plasma torch in the med room. Fortunately for Gillon, a group of Rebels crashed onto the planet soon after the Maid did and, upon being attacked twice by KLR-B1, managed to destroy him and flee the planet with Gillon.