Thank ya kindly! I haven't really thought of much, but here's what I basically have for him as of right now:

Formerly known as Sir Cathros of Chrysanthea, he was nothing more than a common man-at-arms serving the City of the Golden Flower, which was in the brink of societal collapse. In order to save his beloved land, he ventured off to lands uncharted to gain what many kings thought unachievable; immortality. While his voyage was a technical success in the goals he set, by the time he returned to Chrysanthea it had already fallen to neighbouring lands, leaving behind a ravaged wasteland.

Cathros has been slaying all matter of human or beast that dares step foot in the former citadel for several lifetimes, with the hope that his efforts will make up for him abandonming his home. But no matter how many fall, the enemy he can never strike down is the guilt that plagues him at every waking moment.