Race: Demon Lord
Nathrezell appears as an elf with gold skin, brilliant green eyes, straight black hair, and black talons on his fingers and toes. He wears finely crafted black dragon scale armor (very similar in appearance to Aurora's armor, actually), though the only clothing he wears over that is a belt (set with silver skulls), and a cloak (light-absorbing black sprinkled with stars – as if you're not looking at a piece of fabric so much as a cloak shaped hole into the night sky).
Presumably this is not his true form. However, it's the only form that has been definitively associated with him.
(In this case, "**" is being used to represent a value that is - at least by reputation - simply too high to be measured.)
The average person has never heard of Nathrezell. In fact, even the average priest or cleric is mostly unaware of him. This is because he hardly ever interferes directly in mortal affairs; he and his minions are mostly active in the internal politics of the infernal realms. However, for those who have researched such things, Nathrezell is second in dark power only to the Titans themselves - and is certainly stronger than most gods.
Nathrezell is also known to be primarily a manipulator; what another demon lord might strive to accomplish with brute force, he would bring about with but a few words. On the one hand, this makes him safer to deal with in the short term - he is unlikely to simply destroy even the most pretentious of would-be warlocks or the most persistant of foes. On the other hand, it makes dealings with him far more dangerous in the long term.