In the original manga, "King's", "Queen's" and "Jack's Knight" were known as The Three Swordsmen, possessing the maximum speed Summon ability, although they were eventually outmatched by Yako Tenma and his "Summoner Monk".
The main purpose of this series is to swarm the field using the effect of "King's Knight", which can only be activated if "Queen's Knight" is on the field, and is used to Special Summon "Jack's Knight". They are used as Tribute fodder, or are fused to Summon the ultimate monster, "Arcana Knight Joker". Since "King" and "Queen's Knight" are Level 4 monsters, they can easily be used as Xyz Materials for most Xyz Monsters. Given all the members are LIGHT, they can be supported by cards such as "Honest" and "Shining Angel".