The Knights of the Underworld are King Arthur's "conventional" forces in Sonic and the Black Knight; the variety of enemy that Sonic dispatches literally thousands of over the course of the adventure. They are creatures of black magic, and come in a vast array of different forms: from humanoid, sword-and-shield-wielding warriors, to strange helmeted flying fish, to swarms of purple-black bladed spiders, and many in between.
As shown in the game's opening sequence, the Knights of the Underworld are summoned to Grand Kingdom by King Arthur's sword, Deathcalibur. During SatBK's game stages, the Knights frequently warp out of thin air with a flash of black light, and dissolve to nothing after Sonic dispatches them with Caliburn.
It should be noted that the Knights of the Underworld appear impervious to Sonic's standard jump attack, indicating that it is the magical power of Caliburn which banishes them, as opposed to mere physical damage. The Knights can also be defeated with strong sunlight reflected off Caliburn's blade, as seen in Crystal Cave.
The Knights of the Round Table are not Knights of the Underworld, but rather flesh-and-blood knights in the service of King Arthur (at least, until Faraway Avalon). King Arthur himself (eventually revealed to have been a magical illusion created by Merlin) may have been a somewhat more good-natured Knight of the Underworld, as Sonic reports to Merlina that "He disappeared in a puff of black smoke, just like the Knights of the Underworld" after defeating the King on Faraway Avalon.
|Sonic and the Black Knight|