Sammanar

Potentate Sammanar, They-Who-Walk-Unseen, is an Archfey of the Feywild, Keeper of the Sun's Shadow, and Master of the Unseelie Court.

Background
Sammanar is one of five Archfey who has been identified by the Arcana Pansophical.

Campaign One: Vox Machina
During Vox Machina's one-year break, Keyleth, Vax'ildan, Vex'ahlia, Pike, and Tary visited the Feywild and snuck in to watch a performance of the Royal Troupe of the Unseelie Court at the Theater; at the end they apparently saw an "entity" step back into a doorway. Only later did they learn from Percy just how dangerous their trip was, as the Unseelie Court is "the shadow court" and "the thing that the Feywild is a little sketchy about and a little worried about."