The Black Knight is the guardian of Merlin's library in Camelot on PX1-767. The villagers believe that the library is protected by a powerful curse, and all those who enter Merlin's sanctuary forfeit their lives to its guardian. When SG-1 gained entrance to the library with the assistance of Antonius, the village historian, the Black Knight materialized as a holographic image in Antonius's bedchamber and killed him. The knight was activated by the Ancient control pedestal in the secret chamber of Merlin's library, and although it did not appear in the library itself to challenge the intruder, it terrorized the village, keeping people away through fear. When Daniel's attempt to enter a code sequence into the control pedestal caused the holographic knight to reappear in the village, Mitchell confronted the knight in a battle of broadswords. As a hologram, the knight was unaffected by P-90 gunfire or Mitchell's sword, and his sword sliced through Mitchell, causing great pain, although it did not draw blood. Meanwhile, Daniel searched through Merlin's texts for the code to the control pedestal that would deactivate the knight. Finally, in desperation, he fired his handgun at the device's control crystals, shattering them and causing the Black Knight to vanish.
Although not specifically named "Black Knight," a similar holographic guardian was encountered by SG-1 in the caverns of Glastonbury. When Mitchell withdrew the sword from the stone, a holographic knight materialized and engaged Mitchell in battle. The knight was programmed to respond only to the individual who had drawn the sword, making it impossible for SG-1 to come to Mitchell's aid, and as with the Black Knight, each blow from the knight's sword caused great pain. Through sheer determination and force of will, Mitchell defeated the knight, and the hologram vanished. Having passed the test, Mitchell returned the sword to the stone, and Merlin's treasure magically appeared.
Cross Reference: Antonius, Camelot, Glastonbury, Holographic Projection, Merlin's Library, Meurik, Sword in the Stone
Episode Reference: Avalon, Camelot