Hell Hounds are genetically engineered animals, containing characteristics of the Ursine, Feline, Canine, and Reptilian groups, bred for speed and strength in "The Pit" on Kantor Boralis.
When enraged or attacking prey, the colors of their scales change from black to an orange/red. The eyes of the Hell Hounds have properties very similar to Riddick's.
In the last 20 cycles, the Slam Security Network has been adapting the hounds for "enforcement" in the sector's penal system.
In Crematoria Slam Facility, Hell Hounds are periodically released for security purposes and population control (as well as for the guards' amusement) into the Slam Facility at "feeding time", where they indiscriminately attack and devour any inmates that are unable to reach safety in time.
Riddick was able to tame a Hell Hound during feeding time by simply staring it down, leaving The Guv perplexed as to how he had accomplished such a feat, to which Riddick replied "It's an animal thing."