Kir Kanos was a former Emperor's Royal Guard who slew would-be Emperor Carnor Jax and eliminated the Imperial Ruling Council, whom he believed had caused the Emperor's death. He later encountered Luke Skywalker, who finally convinced him to give up his hate and anger. He lived as a recluse afterwards until the invasion of the Altarin'Dakor into Epsilon Sector, after which he fought for the New Imperium against the invaders.
Kir Kanos had an illustrious career before he ever came to the New Imperium. Highly in-depth information can be found on the Kir Kanos page in the Star Wars Wiki.
The New Imperium Edit
After his encounter with Skywalker, Kanos faded into obscurity, hiding on the planet Haven in the Satyr System and calling himself by the name of Jac Railler. He lived a simple life there until the planet was attacked by the Altarin'Dakor. He could never truly escape who he was, however, a truth he learned when the Altarin'Dakor attacked the planet and kidnapped most of the population. Kanos managed to save a few and escape via shuttle to Varnus, where he warned the NI of the unstoppable foe that had come upon them. Kanos stayed on Varnus from that point on, though he teamed up with Maarek Stele long enough to and rescue a few more settlers who had been abandoned on Haven.
When the Altarin'Dakor invaded, Kanos saw first-hand their brutality and ruthlessness, and the fire inside him returned. Grand Master Xar Kerensky noticed him and, discovering his true identity, convinced Kanos to help train the Royal Palace Guard and the Varnusian Defense Force. Kanos agreed, and served in Vectur until the Battle of Varnus, during which he played a key role in defending the palace from the enemy. Also during the battle, his long-supressed Force abilities finally manifested themselves, just in time to save his life and that of several Jedi. He went on to survive the battle, though after that was uncertain whether or not he could continue fighting. The destruction he'd seen was so great, a capstone to a career of violence, and he truly felt that he was at a crossroads in his life, with a major decision ahead to continue on the same path, or to seek something new that would finally, possible, give him peace and rest.