You guys passed the knowledge checks... at least in part. You probably saw some mention of Zarren in some books at Sigurd's Keep.

Here is something you guys found out about the demon Zarren. He is an ancient kelvezu, a race of demons who serve demon lords as elite assassins. Once, many centuries ago, he was sent to Midgard kill a powerful champion of Good - a silver dragon. Said dragon was prepared for the assassination attempt, and Zarren failed horribly, having to flee Midgard in shame or this failure, he was imprisoned by his master.

Fast forward to around the time of Ragnarok. Azrashak, the demon lord, required the services of a master assassin. So Zarren was freed and given a new mission. He was summoned to Midgard at a special location. Here the text makes mention of an elaborate plot by Azrashak involving this location, but does not give details. In any case, he was summoned to Midgard to serve as an enforcer and bodyguard to Azrashak's vanguard, the demons who were to prepare the way for their lord's arrival in Midgard. Their activities were interrupted by some human adventurers. Zarren and the other demons battled the human heroes but were driven off and never heard from since.

The end.

Kelvezu demon (powerful demonic assassin); associate of Isidor (Ustyhrin-ja).

Research by Vasily, Nikolai, and Juliane has revealed the following:

(source: this forum thread)

"NOTE: This is in addition to what Anait? already told you. That is to say: some of what you discover in your ongoing research overlaps with what Anait? told you to some degree, and I won't repeat existing info."

Knowledge (history)

Zarren was one of an ancient sect of demonic assassins that tapped into the essence of the Shadow Realm? for their powers. Some say they started out as humans, in a time in the distant past, but lost their souls to Shadow and became demons thusly. Since time immemorial, Zarren's kind had been highly sought after as living weapons by baatezu? demon lords. He is one of the last (or perhaps the last) of his kind; the others were killed, one by one over the centuries, mostly by celestials.

Before the events surrounding Ragnarok, the last time Zarren was seen in Midgard?, or heard from at all, was when he was sent to assassinate the silver dragon Sa'ari, almost six centuries ago. Zarren's failure in that mission is what led to his fall from grace and imprisonment until Ragnarok. Serving Azrashak? was Zarren's only chance for regaining his freedom and status in the demonic hierarchy.

Knowledge (the planes)

Zarren's race are called kelvezu?, and they are naturally adapted for stealth and assassination. Like rogues, they are experts at sneak attacks; they have a talent for evading area-effect spells and cannot be flanked nor surprised; they have uncanny vision, able to see in darkness, discern magic effects, see through invisibility... kelvezu weapons are coated with deadly poison. In a word: they're assassins, possessing all the skills of a highly trained rogue augmented by infernal toughness and defenses, as well as rudimentary demonic magic.