Shinryu

Shinryu also referred to as Lord Dragon or Nova Dragon, is a powerful dragon entity and a recurring extra boss in the Final Fantasy series. In the Dissidia: Final Fantasy series however Shinryu serves as the overarching antagonist, manipulating the cycles of war between Cosmos and Chaos to increase his own power.

Shinryu is a god-like being who dwells within the Dimensional Rift. When Cid of the Lufaine, Cosmos and Chaos first arrived in World B they came across Shinryu and made a deal with him so they could return home. The deal resulted in the beginning the cycle of war between Chaos and Cosmos, where they would summon warriors to battle one another in a divine conflict.

Dissidia: Final Fantasy
Alongside Cid, Shinryu was an observer of the cycles of war between Cosmos and Chaos. Shinryu manipulated the cycles of war so that he would grow more powerful from it. When all warriors of one side were killed, Shinryu would revive all those killed on both sides and devour their memories to become stronger. Shinryu also gave Chaos with some of its power causing him to over time grow into the ultimate weapon. Once Chaos reached that point Cid intended for the three to return home and for Chaos to destroy that which had caused them to war. Shinryu also granted Cid immortality to observe the cycle, though at the cost of his physical form.

During the thirteenth cycle, after Cid broke their pact of neutrality and sided with Cosmos to end the cycles of war, Shinryu retaliated by assisting Chaos in the final battle with the Warriors of Light. After Chaos killed by the warriors of Cosmos, Shinryu absorbs his strength and returns to the Rift, his pact with Cid complete.

Dissidia Final Fantasy NT
After the end of the war between Cosmos and Chaos, Shinryu departed to the rift. But when a new war began in World B, Shinryu returned to further manipulate the war and absorb the energy generated by the fighting heroes to empower itself. Eventually, the two sides would come together to stop Shinryu and it to free World B from its control. With the combined strength of the summoned warriors of Materia and Spiritus, Shinryu is destroyed, ending his destructive reign over World B.