Sammanar

Potentate Sammanar, They-Who-Walk-Unseen, was an Archfey of the Feywild, keeper of the Sun's Shadow, and Master of the Unseelie Court. As of 812 PD, they were among the five Archfey identified by the Arcana Pansophical.

Background
Sammanar is one of five Archfey identified by the Arcana Pansophical, one of whom has since died.

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."