Hythlodaeus appears much like the shades of Ascians that populate Amaurot in the Tempest. He towers over the Warrior of Light and the Scions of the Seventh Dawn, wearing the signature Amaurotine gray robes and half-mask.
Despite being aware of being a Shade, Hythlodaeus chooses to continue as normal, aware that he cannot change anything as he is. He is civil when talking to the Warrior of Light, and seeks only to confirm the Warrior's resolve.
In Tales from the Shadows, Hythlodaeus was said to be friendly but incurably smug for little escaped his perception and ability to perceive the Underworld as well as the intent, form and aether of others. He also often teased Hades with coy remarks and wide grins, but nevertheless immensely respected his close friend. He was also humble, having denied the title of Emet-Selch despite being the keener of the pair.
When the Warrior of Light is confirming his entry into the Capitol to confront Emet-Selch, they are assaulted by the Light stored inside them by the Lightwardens. The pain subsides when Hythlodaeus asks the Warrior to sit next to them, distracting them from the pain.
Hythlodaeus reveals that he knows he is a Shade, theorizing that Emet-Selch made a mistake while making him, indicating that they were friends once. Hythlodaeus suggests that he can see Ardbert, if only ephemerally. Hythlodaeus touches on the catastrophe that awaited the ancient Amaurotines of the original world and calls it The Final Days. He describes the nature of the incidents transitioning from isolated and non-related into a world-spanning threat.
The Convocation of Fourteen—which at the time was Thirteen—endeavored to create a will for the star that required vast amounts of aether, provided willingly by an already decimated Amaurotine population in the name of salvation. It took nearly half of the remaining Amaurotines and birthed Zodiark from their sacrifice, halting the calamity. Hythlodaeus wistfully reveals that the star had suffered so much that restoring life to its surface required Zodiark to be summoned yet again, further halving the remaining Amaurotine population.
After stating that he recognized the "color" of the Warrior's soul, Hythlodaeus vanishes.
His name came from Raphael Hythlodaeus, a character from Thomas More's Utopia.