The Daemonslayer, the White Knight of Gaia, the Sword of Light, even the Sword That Smites Evil - Ren is all of it. Once just a newbie adventurer, Ren is now a member of the Holy Order of Asheron - one of the three Terran Holy Orders fighting against the ruinous powers that constantly slip into the mortal world from the Nether (yes, most of the members of these Orders are humans; there are some enkidu like Ren there, though - at least in the Asheronian and Everestian Order). Ren has some impressive powers like the Aura Sword - an energy blade created through sheer will, while some other of his powers some would consider.. unnatural (just kidding; it's just that he can transform into a Daemon - a Hell Knight, to be precise).
Ren is generally a nice, if a bit reserved guy. However, on the field of battle he sometimes changes completely, especially if he is fighting against some Daemons (note Demons and DAEMONS are not one and the same in the "ASoG" - Demons are Altlings, while DAEMONS are creatures from the Nether) or is really angered. In this case he goes all out against his opponent, fighting without holding back and tearing apart everything in his way (as long as it is not some living being). But more often than not he would rather try to keep his opponent alive.