The Black Knight is the titular main antagonist of the Power Rangers Time Force episode "Beware the Knight".
He steals a box with the power for the Red Ranger's Battle Warrior from a White Knight but due to his evil heart, he could never open it. He rides a horse in black armor.
Centuries later, he seeks a warrior with a pure heart to open the box for him
Wes destroys the knight with the Battle Warrior armor and seals the cave by sticking the knight's sword into the ground.