Saundor

Saundor was an archfey living in the Shademirk Bog in the Feywild and the former owner of Fenthras, Wrath of the Fey Warden. Betrayed and forgotten by his lover, Saundor was left to his own despair, corrupting the Shademirk Bog. Residing inside an enormous tree in the middle of the bog, Saundor longed for someone to heal his wounds and cleanse his heart:  a companion, a friend. As an NPC, he was played by Matthew Mercer.

Description
Saundor was a thin, elf-like individual covered in a mass of plants, leaves, and thorns. The only flesh-like portion of his body was his face. His eyes glowed bright yellow. He could connect his body to the tree he resided in through tendrils of plant matter that attached to his back and shoulders.

Encounter with Vox Machina
While in the Shademirk Bog, as part of Vox Machina's preparations to enter the cancerous tree rumored to contain Fenthras, Keyleth cast Commune with Nature to learn about the tree. Asking the environment what was fueling the tree, she heard the name "Saundor" for the first time.

Trivia

 * Matthew Mercer's character sheet for Saundor was briefly shown in "Behind the Screen", the ninth episode of GM Tips with Matt Mercer, with his name spelled as "Sondur".  The character sheet was written before, and after that episode, Matt stated twice on Twitter that the correct spelling is "Saundor".   This wiki uses the more recent "Saundor" spelling.
 * Travis Willingham speculated that the tree used to be a person whose heart was broken, which was not far from the truth.