Algernon is a special rat NPC, he has a green tinted nose. He's much faster than almost any other mob, and bites rather hard.

He drops an already identified gem. 

Algernon is a reference to a short sifi novel titled "Flowers for Algernon", written by Daniel Keyes. The book is about a lab rat named Algernon, and a boy named Charles, both of which are given increased intelligence via artificial means. The book was published in 1958, a novel was published in 1966.