The Black Knights began as a rogue terrorist group in Area 11 (formerly known as Japan) to fight against the Britannians. They were a no-name nuisance to Britannian forces for the most part, possessing a single Knightmare. But when a mysterious man comes along, known only by his voice, began issuing orders to these terrorists, the tide begins to turn. The man delivers them multiple Knightmare frames and, with amazing strategic talent, defeats the Britannian forces in the Shinjuku ghetto.
Soon after, the mysterious man reveals himself to be "Zero," a masked man intent on destroying Britannia and bringing "justice" to the world. With that, the terrorists changed their intentions: they wouldn't simply irritate the Britannians - they would liberate Japan. To that end, they were given a new hideout, Knightmares, technology, uniforms, and a name - the Black Knights, knights for justice.