The miner's horror was a large, space-borne creature of mysterious origins. Often over twenty meters in size, they were vaguely fish-shaped, with large dorsal spines and a set of large, saw-like teeth. They fed on asteroids, which they chewed into dust and slowly digested and refined into the pure metals and minerals which nourished them. Over decades, a miner's horror could eat entire asteroid belts.
As they were constantly hungry, they were a significant hazard to inhabited asteroids, space stations, and spacecraft, which they would devour for their metallic content. Luckily for most spacers, miner's horrors were fairly easy to outrun. If they could not be outrun, however, they were difficult to destroy. All the same, mining companies sometimes sponsored hunting expeditions in order to recover refined ore from a horror's body.
It was uncertain where the miner's horrors originated: the Outer Rim Territories, the Unknown Regions, Wild Space, or even extra-galactic space. The first recorded miner's horror was encountered by a group of pirates in the Galactic fringes circa 5000 BBY. Their reports were not believed, until the remains of a starship attacked by one of the beasts was discovered. Two armed freighters went after the creature, with only one returning intact.
Since then, rare sightings of miner's horrors continued. These were all sightings of lone creatures, save one sighting of three horrors eating the wreckage of a recent battle. (This part of space was, of course, avoided thereafter by prudent astrogators.) Over time, the sightings became closer and closer to the central parts of the galaxy, though the most central sightings in the Imperial Period were in the relatively remote Tion Cluster. Some believed that the miner's horrors were part of a very slow-moving invasion force, and that larger miner's horrors than the freighter-sized creatures encountered to date were on the way.