The Black Knights (黒騎士 kuro kishi), also referred to as Dark Knights (暗黒の騎士 ankoku no kishi) or Dark Rocket Knights ((暗黒のロケットナイト ankoku no rokettonaito), are a rebellious group of Ex-Rocket Knights. Unlike the Rocket Knights the Black Knights don't serve any kingdom and king for long and rather live their lives as mercenaries, willing to accept any sort of work as long as it benefits them the most.
According to the game manual of Rocket Knight Adventures (US/EU Version only) the Black Knights are a band of Rocket Knights gone bad, as power and greed corrupted them.
It is unknown how many Black Knights really exist. So far Axel Gear is the only known one and seen as the "leader" of Black Knights, and according to the game manual of Sparkster: Rocket Knight Adventures 2 (US/EU Version only) he wants to hunt down all of the remaining members of the Rocket Knight corps.
List of Black Knights
Current Leader of Black Knights
Other members of Black Knights