Riddick is a criminal on the run from all sorts of people and authorities, but exactly who he refuses to mention. While he's happy to fight other humans, he prefers to try out his exceptional night vision on the lethal critters of the wasteland.
Riddick is a reference to Richard B. Riddick, the titular main protagonist in the Chronicles of Riddick science fiction universe. His appearance and abilities are much the same; including Night Vision. The encounter title Pitch Black is a reference to the first film in the series, in which Riddick combats nocturnal alien monsters during a solar eclipse on the planet where the ship transporting him had crash-landed.