The most famous group from the Arthurian Legends are the renowned Knights of the Round Table.
The Knights of the Round Table are the legendary knights of the fellowship of King Arthur that first appeared in the Matter of Britain literature in the mid-12th century. The Knights are an order dedicated to ensuring the peace of Arthur’s kingdom following an early warring period, entrusted in later years to undergo a mystical quest for the Holy Grail. The Round Table at which they meet is a symbol of the equality of its members, who range from sovereign royals to minor nobles.
References:
The Knights of the Round Table have made appearances in many media especially when the time period is around King Arthur’s time. There are a few that are very much inspired by them.
Final Fantasy:
In Final Fantasy series they have appeared in two different forms.
Knights of the Round in Final Fantasy 7. The most powerful summon in the game made of 13 knights.
King Thordan and his Knights in Final Fantasy 14. A powerful boss in the Heavensward Expansion.
Digimon:
Digimon has a group of 13 Digimon that protect the Digital World while carrying out orders from the God of the Digital World, Yggdrasil.