Ragnarok is also one of the running items of the
Final Fantasy series. It is usually the strongest
sword that can be found, though it varies from game to game.
As far as it's known, its first appearance was in Final Fantasy 3, as the strongest sword available. It is found in the Forbidden Land Eureka, after defeating the Guardian.
In Final Fantasy 4, it is Cecil's strongest sword, gained by defeating Bahamut in the moon core.
In Final Fantasy 5, Ragnarok is hidden on the Cleft of Dimension, guarded by the greatest of all dragons, Shinryuu. Ragnarok is a very powerful sword.
In Final Fantasy 6, Ragnarok can be got as either a weapon or as an Esper. Ragnarok sword is powerful and can be traded for the even more powerful Illumina, but the Ragnarok Esper is the only one that will teach you the most powerful spell in the game: Ultima.
In Final Fantasy 7, it is merely the second most powerful sword available for Cloud. Six materia slots, set in pairs.
In Final Fantasy 8, Ragnarok is the name of the spaceship you use to move around the overworld. Pffft.
In Final Fantasy 9, it apparently is the second most powerful sword again, used by Steiner. What do they have against it?