He is a bastard son of one of the Royal Seven Houses, who evidently used to rule the world. The actor, Sasha Roiz, also clarified what CPT Renard is in this interview
. I did not pick up what the transformation was meant to show from what we saw in "The Kiss", but I guess I was hoping for something else. The Royals apparently employed Grimm when possible and had specially trained folks to kill other Grimm (presumably unaligned Grimm as well as the Grimm of your enemy). The next best thing to employing a Grimm, is to control and influence one...
Grim vs Reaper. Seems like balancing character classes in video-games.