The Researcher

The Researcher is an NPC that appears once 10 Unique Monster species have been identified, and every lot of 10 monster species you inspect after that.

When he appears, the Researcher greets you with either- The Researcher gives you a key fragment for you troubles and can act of his own accord when you move out of sight of him.
 *  'We've been looking all over for you! Your daring expeditions have done wonders for our understanding of local fauna.'

It is possible to receive quests from the Researcher, although they appear to be general NPC quests

Its is possible to kill the Researcher, however, he does not drop anything