Darth Laut
Once, he was a mere Dark Side Adept. He stumbled across J'ror Tholin, Rand Al'thor? and the others in their party. Rand cut his leg off. He swore vengance, got a cybernetic leg, tracked them down, and Rand cut his other leg off. Burning with rage, he got a new cybernetic leg, swore bloody vengance, and managed to track them down once more. Rand cut both his arms off.
This made him stop and think for a bit.
He retreated into the unknown territories with a ship and wasn't heard from for a while. Eventually, rumors of a nascent Sith Empire forming beyond the Outer Rim? worked their way into the hands of the Jedi Council. They sent a group of young Jedi Knights? to investigate, and they were never heard from again. This was right before the events on Andijon, where it became apparent that he had developed a small industrial base and was attempting to acquire Sith artifacts to enhance his power. He had a student, Tvlashka, who had a student, At'!'chk, who was a genius droid designer.
However, despite capturing Zeltar Hale, he was surprised by the focused attention of Nakail, who cut his cybernetic body in half, nearly killing him, and getting away with the spirit of Bellisarius. Chasing after Nakail, Laut was in turn defeated and swore allegience to the Pain God. From then on, he loyally served his new master, providing him with an industrial base and hidden shipyards to use for his attack against the Galactic Republic.
When Bellisarius was defeated, he found himself in control of a large swath of the galaxy. Vowing to continue his master's efforts, he focused on developing a weapon so powerful, nothing could defeat it. He arranged for the control of most of the Empire's artificers to be focused on this project, sequestering them away from his rival Davrosh. Only the wandering Prophet Enati could forsee what was to come, and he had disappeared from the explored galaxy for his own reasons.
And thus was born the Dark Swarm.