Boris Nagorny was the gunnery officer on board the Nostalgia for Infinity from an unknown time until 2543. During his time aboard he became romantically involved with Sudjic, another member of the crew.
After being linked directly to the ship's gunnery station through neural implants, Boris began showing signs of mental instability; particularly, obsessive behavior revolving around something he called "Sun Stealer". It was only discovered years later that Sun Stealer was actually an alien-manufactured computer entity that had been trapped in the gunnery systems by their automated digital defenses, and had tried to break free by mentally influencing Nagorny.
Ilia Volyova, the woman who trained him in weapons control, killed him in 2543, after he proved to unstable and dangerous to be allowed to live.