Great Cataclysm

"I am Aginah. I sense something is happening in the Golden Land the Seven Wise Men sealed... This must be an omen of the Great Cataclysm foretold by the people of Hylian blood..."

- Aginah

"The Hero's triumph on Cataclysm's Eve wins three symbols of virtue. The Master Sword he retrieves, keeping the Knight's line true."

- Pedestal of the Master Sword

On Cataclysm's Eve
The Great Cataclysm is the name given to an event that occurred in Hyrule's history that involved Ganon's entry into the Sacred Realm and his theft of the Triforce. The inscription on the pedestal of the Master Sword reads: "The Hero's triumph on Cataclysm's Eve wins three symbols of virtue. The Master Sword he retrieves, keeping the Knight's line true." Some believe this refers to the Link of A Link to the Past, who was destined to triumph over Ganon and reclaim the Triforce, preserving the bloodline of the knights who fought against Ganon during the Imprisoning War. The Maiden Link rescues in the Skull Woods further explains that the prophecy of the Great Cataclysm means that whenever an evil person seizes the Triforce (as Ganon did during the Imprisoning War), a hero is destined to rise up and vanquish the evil one. Furthermore, the prophecy states that the hero must be of the bloodline of the Knights of Hyrule. This seems to indicate that the Cataclysm ends with the battle between the Hero armed with the Master Sword and the evil person holding the Triforce.

In the instruction manual for Link's Awakening, another reference to the prophecy is made. Link "fulfilled the Hyrulian prophecy of the Legendary Hero and destroyed the evil tyrant Ganon." However, while this prophecy speaks of undoing the evils of the Great Cataclysm, it does not define exactly what the Great Cataclysm was, giving rise to multiple ideas of what it may refer to. While some believe it refers to the events of A Link to the Past itself, others believe it refers to Ganondorf's entry into the Sacred Realm and his hauling of the Triforce depicted in Ocarina of Time, as discussed below.

Theory
Some believe that the Great Cataclysm itself however refers to the prophecy of the Hero of Time, the Master Sword's first true wielder and the Hero that was present at the time of the Great Cataclysm itself (thought also to be the opening of the Sacred Realm and the shattering of the Triforce, hence the term "cataclysm"). The Hero of Time triumphed over the evil monsters created by the Dark Lord Ganondorf on the eve of the Cataclysm (literally, as Ganondorf's entry into the Sacred Realm took place almost immediately following the Hero's success in gaining the Spiritual Stones) and won three objects, the Spiritual Stones, that were required to open the way to the Master Sword. Despite the Hero's triumph and his claiming of the Master Sword, this enabled Ganondorf to unleash the Great Cataclysm, which shattered the Triforce and altered the course of Hyrule's future for ages to come as the Triforce pieces remained divided for eons and Ganondorf attained immortality of sorts, giving Hyrule an unrelenting threat to its existence that would persist for ages to come and beyond. While it would be a retcon of the original story of A Link to the Past, it only makes sense that a "cataclysm" is some "cataclysmic" event that leads to disaster, and in this case, Ganondorf's entry into the Sacred Realm proved to indeed be one of the greatest "cataclysms" in Hyrule's history, given the consequences Hyrule suffered thanks to it. It is also no surprise that a prophecy was made about a new Hero that would completely erase the devastating effects of the Great Cataclysm and destroy Ganon utterly, the Link of A Link to the Past. However, the Hero spoken of in the legend of the Great Cataclysm itself seems almost certainly to have been the first Hero that was actually present when it occurred, the Hero of Time.

While not considered official, the Hero of Time is said to be descended from the Knights of Hyrule that guarded the Hylian royalty through his father's side in the manga of Ocarina of Time. This gives further rise to the possibility that he could be the Hero spoken of in the legends of the Great Cataclysm. While A Link to the Past is the first game to speak of the Great Cataclysm and one of the Maidens speaks of a prophecy regarding it, neither expressly states what exactly the Great Cataclysm was, though from its name it would seem to be some sort of "cataclysmic" event that took place in the land of Hyrule at some point. Considering the consequences that followed after Ganondorf broke into the Sacred Realm and hauled the Triforce, this would seem to be one of the greatest "cataclysms" in Hyrule's history. The prophecy spoken of by one of the Maidens seems only to have been speaking of one who would undo the evils wrought by the Great Cataclysm rather than speaking of what the Great Cataclysm itself was. The story of Ocarina of Time seems to have been crafted to explain the events spoken of in the history of the Imprisoning War and the Great Cataclysm in A Link to the Past. In addition, the Maiden clearly stated that "when an evil person gains hold of the Triforce," a Hero is destined to appear of the bloodline of the Knights of Hyrule. Ganondorf is shown to have first gained the Triforce in Ocarina of Time, and a Hero (arguably one of the greatest ones in the history of Hyrule) did indeed rise up to defeat him and seal him away. Considering that many generations separate Ocarina of Time from A Link to the Past, this makes it all the more likely that the Hero of Time is the Hero spoken of in the legends of the Great Cataclysm and that the Hero seen in A Link to the Past was the one spoken of in the later prophecy that would be the one to ultimately undo what had been done by the Great Cataclysm.