From: Star Trek: The Original Series
Caption: The Black Knight.
Medieval armor-clad horseman who appeared on the amusement park planet as a manifestation of the thoughts of Yeoman Tonia Barrows. The black knight was among the characters imagined by the Enterprise landing party and replicated from cellular castings manufactured beneath the planet. The black knight attacked Dr. McCoy with a lance and apparently killed him; however, the good doctor was taken underground and "repaired," coming back good as new.