The SSITH was unique in that it employed state-of-the-art solid-state hologram technology to create a full-scale lightsaber combatant. This in turn could then be programmed to employ specific training programs and execute complex combat algorithims for training purposes.
They were first employed on the secretive Jedi Praxium on Thule, and used to train the Jedi initiates who had been assigned there.
The SSITH was developed by Jedi Knight Kol Halcyon. Halcyon was well-known within Jedi circles as a skilled engineer and tinker from the Corellian Sector. After the outbreak of the Clone Wars and the emergence of lightsaber-wielding combatants, Halcyon saw the need for a more practical tool for training one's skills in one-on-one lightsaber combat.
Using data from ancient Sith holocrons stored in the Jedi Archives, Halcyon recreated Darth Nihilus and Darth Revan as solid-state holo-matrixies endowed with advanced droid brains. They were capable of executing highly-complex combat programs and algorithims that adapted to suit the individual using the SSITH for training.One of the primary benefits of the SSITH was that it was able to be used in a non-lethal way; the blade of a SSITH's lightsaber could be adjusted from a non-lethal low-power setting, so as not to cause any real harm during training exercises, to a far more high-powered one capable of effectively simulating a real blade. This made the SSITH perfectly suited as training companions for users of any level of skill from raw initiates just learning to weild the traditional Jedi weapon to seasoned masters looking to keep thier skills sharp.
Halcyon entrusted the technology to his friend, Jedi Master Caff K'iron. K'iron was well known for using unorthadox training methods, and Halcyon believed that he would be the perfect individual to test out the new technology. Unbeknownst to Halcyon, K'iron used the SSITH as part of the regular training regimin for his secretive training facility on the planet Thule.