Endrin is the headmaster of the Athenaeum, the school of sorcery located in Shadowhaven. He is a powerful sorcerer, and also quite physically adept for his age, due to being a former scavenger.
After analyzing the water given to him by the heroes, Endrin invited the characters to a dinner party, where they spoke to the entire faculty about their exploits. During the party, Endrin (Glowborn) was poisoned and nearly died. The poison, being elven in origin made Sneparious Thorntongue the suspect of the murder attempts.
Endrin, believing this to be too convenient, asked the heroes to make an independent investigation, which uncovered a plot by the Requiem and cleared Sneparious. Endrin and the rest of the school were grateful. The heroes had made a strong ally.