From Halopedia, the Halo wiki
Knight Champions are a class of Promethean Knights.
In Warzone simulations, Knight Champions have the same appearance as a Knight Commander, thus Champions have the hardlight blade they do, have several spikes sticking up from behind their heads, and sport a white color scheme (orange and turquoise for Legendary variants).
In Warzone Firefight, Knight Champions appear in the final round in either Attack on Sanctum or Urban, where they appear as Legendary Knight Commanders armed with the River of Light. Defeating them will grant the participating players a Legendary Takedown medal for each Champion killed. In Attack on Sanctum, they appear alongside a Mythic Warden Eternal duo, making the match much more difficult to complete due to the many Incineration Cannon-armed Knights spawning in as minions.
List of appearances