The Knights of the Round are a group of primals from Final Fantasy XIV: Heavensward in the form of Archbishop Thordan VII and the Heavens' Ward, using the power of Nidhogg's eye to assume the form of King Thordan and his Knights Twelve.
The Knights of the Round are based on the ultimate summon from Final Fantasy VII, though are no longer the actual Arthurian knights. Thordan is the most unique among them, with all the rest bearing similar appearances to one another, save for mage knights sporting different dress from the martial knights.
In the "alternate timeline" of Dragonsong's Reprise (Ultimate), after absorbing Hraesvelgr and Nidhogg's eyes, King Thordan becomes Dragon-king Thordan. As Dragon-king Thordan, his armor becomes organic and scaled with a white glow, and wields three copies of the sword Ascalon, with one held in the mouth of a long draconic tail.
King Thordan and the Knights Twelve are fought as the final bosses of Heavensward expansion at The Singularity Reactor. They wear armor and use abilities similar to those seen in the Final Fantasy VII summon. While King Thordan is the main enemy in the encounter, he uses an attack called Knights of the Round to summon the other knights (who then use one of their own moves, often being a holy or upgraded version of an existing job's abilities) throughout the fight and uses Ultimate End as a last ditch attack towards the end.
In the Minstrel Ballad version of the fight, Thordan uses Knights of the Round in the last phase several times, calling different knights to his aid each time.
King Thordan and the Knights Twelve are fought multiple times in Dragonsong's Reprise (Ultimate) in Endwalker. Sers Adelphel, Grinnaux, and Charibert are the first encounter of the raid. King Thordan is first encountered in the "main timeline" in the Singularity Reactor. He is fought again in the "alternate timeline" after saving Haurchefant Greystone from his death in the main storyline. After reaching a low percentage of his health, King Thordan will plead for mercy. If spared, he returns to absorb Hraesvelgr and Nidhogg's eyes following their defeat, becoming the final boss of the encounter, Dragon-king Thordan.
The battle theme of the Knights of the Round is titled "Heroes". A live recording of "Heroes" is the sixteenth track on the A New World: intimate music from Final Fantasy - Volume II album. In Dragonsong's Reprise (Ultimate), Dragon-king Thordan is fought to the Eorzean Symphony rendition of Revenge Twofold.
In the Japanese version, King Thordan has a different title: "Kishin Thordan" (騎神トールダン). Rather than a king, his title literally translated to "Knight God".
Knights of the Round Table are the main characters in the Arthurian legends of Britain. King Arthur was the leader of the knights, wielding the sword Excalibur. When called, the knights assembled at the Round Table. According to legend, Arthur was betrayed by Mordred, in some accounts held to be his own son. Arthur assembled his knights to a battle to the last man with the traitor, in which Mordred was slain and King Arthur was fatally wounded. Sir Bedivere, the only survivor, took the King to Avalon to rest until he was needed to rule Britain again.The