King of Hyrule

The King of Hyrule was a wise ruler of the kingdom of Hyrule long in its past that was featured in the backstory of. He ruled over a golden age for the kingdom by selflessly wielding the united Triforce as a tool to govern the land. However, as his death neared, the King shattered the Triforce into its three component parts and concealed the Triforce of Courage within the deepest recesses of the Great Palace in the Valley of Death, guarded by many powerful monsters. He then cast a spell across the entire valley that would prevent entry until six magical crystals were restored to six special statues kept in six other palaces across Hyrule. Before he died, he confided what he had done to his daughter, Princess Zelda, but kept his son, the Prince of Hyrule, in the dark about it.

After the King’s death and the Prince’s ascension to Hyrule’s throne, he was angered to see that he could only inherit the Triforce in part. Though he searched high and low for the missing piece, he could not find it. Not long afterward, an evil magician that had served in the King’s court revealed to the Prince that his sister, Zelda, knew a secret about the whereabouts of the other Triforce piece, causing the two to confront her about it. When she refused to talk, the magician cast her into an eternal slumber and died from the backlash of the powerful spell he’d cast. To commemorate this tragedy, the Prince decreed that from that day forward, every female member born into the Royal House of Hyrule would be named Zelda.

Biography
In the backstory of The Adventure of Link, it is revealed that there was once a great and wise King of Hyrule that governed the land with the strength of the united Triforce as his command. As his heart was balanced and true, he was worthy of possessing the Triforce as he used it selflessly in service of the people of the kingdom and not for merely his own gain. However, the King too was human, and there came a time when he became frail as his days became numbered. Anticipating his death, he began to arbitrate as to what to do with the Triforce before his death could result in it changing hands. Knowing that great evil would befall the land of Hyrule if the Triforce fell into the wrong hands and knowing the weaknesses of his own son, the Prince of Hyrule, the King hoped to find someone with the innate qualities that were fitting of a worthy possessor of the Triforce. Unfortunately, he was unable to find any such person during his lifespan that had no evil thoughts and possessed those qualities he sought. Since his own son did not fit this archetype for being worthy to possess the one true Triforce, the King elected to split the relic into its three component parts, leaving the Triforce of Power and the Triforce of Wisdom within the kingdom.

The Triforce of Courage however shared a different fate than that of its counterparts. In secret, the King spirited this piece of the Triforce away to the distant and dangerous Valley of Death, where he concealed the relic within the deepest sanctums of the Great Palace that was set at the head of the valley, guarded by many powerful monsters handpicked by the King himself. The King cast a magical barrier over the entire Valley of Death, one that would not grant entry to the valley until six special crystals were restored to their respective statues in six other palaces that lay across Hyrule. He also secretly cast a spell over all of Hyrule, one that would, at some point in time when a worthy person was born and came of age, cause the symbol of the Triforce to appear on the back of the hand of this special individual, marking him as the King’s chosen person to reclaim the Triforce of Courage. Soon after this, the King’s time was drawing to a close, and before he died, he confided what he had done only to his daughter, Princess Zelda, choosing to not tell any of the secrets of the Triforce to his son.

After the King’s death, the Prince of Hyrule hoped to claim the Triforce and wield it as his father had done, but he was angered and dismayed to find that he would only inherit it in part. He searched the kingdom high and low for the third piece, but he was unsuccessful in this endeavor. It was at this time that a mysterious magician that had been close to the King revealed to the Prince that the King had told a secret about the Triforce to his sister, Princess Zelda. He immediately questioned Zelda about what their father had told her, but she refused talk as their father had not wanted him to know anything, having deemed him unworthy. The magician then threatened to place Zelda into an enchanted slumber unless she divulged the King's secret, but still she refused to tell them anything. Though the Prince tried to stop him, the evil magician cast an extremely powerful sleeping spell upon Zelda, causing her to drop unconscious and himself to fall dead from the magical backlash of the spell. In his grief, the Prince had Zelda’s body moved to a special room in the North Castle, to rest behind a magical door that would only open for one possessing the symbol that would mark them as the only one capable of finding the last Triforce piece and thus wake Zelda from her eternal sleep. To commemorate this tragedy, the Prince decreed that henceforth, every female child born into the Royal Family of Hyrule would be named Zelda in honor of his fallen sister.

Many long years following these tragic events, the heroic boy known as Link basked in the wake of his triumph over Ganon in that took place several seasons before. His sixteenth birthday eventually arrived, and to his astonishment, a strange crest of a triangle made up of three smaller triangles appeared on the back of his hand. Puzzled by its meaning, he consulted Impa, the nursemaid of Princess Zelda. Impa was awestruck to see the symbol, as her family had been on the lookout for the individual that would possess this crest across many generations of their family. She took Link to the North Castle and to the so-called "Door That Does Not Open". She took Link's hand and pressed the symbol upon the door, and to Link's surprise, he heard the door's lock falling open. Inside, he saw the beautiful Princess Zelda from an age ago still sleeping peacefully upon an altar in the center of the chamber.

Impa began to relate to Link the "Legend of Zelda", which spoke of the ancient King and how his actions before his death had ultimately resulted in his daughter's fall into a slumber from which she may never awake. The only known thing powerful enough to break the curse upon Princess Zelda and restore her to life Impa revealed was the united Triforce. To this end, Impa gave Link a chest with a similar crest on it, containing the six special crystals and an ancient scroll written by the King himself, detailing the secrets of the Triforce. Though it was written in an ancient form of Hylian, Link discovered to his surprise that he could read the ancient text, which read as follows:

'You who'll control the Triforce of the future. I shall hand down to you the secrets of the Triforce. There are three kinds of Triforce - Power, Wisdom, and Courage. When these three are brought together, the Triforce will share its maximum power. Of the three, I have left Power and Wisdom in the kingdom. But the Triforce of Courage I have hidden for a reason. Not everybody can use the Triforce. It requires a strong character with no evil thoughts. But an inborn special quality is also necessary. Unfortunately, I have not found such a person during my lifetime.'

'Therefore, I have decided to cast a spell on all of Hyrule. A crest will appear on a young man with that character who has been brought up correctly, has gained many kinds of experiences and reached a certain age. But, what will happen if someone else uses the Triforce before then? If it is misused, it will produce many evils.' 'The Triforce of Courage is hidden in the Great Palace in the Valley of Death on the largest island in Hyrule. However, to enter you must first fight the guardians and undo the 'binding force.' When you have defeated the guardians, which I made to prevent enemies from invading the six palaces in Hyrule, set a crystal in the forehead of the statue you find. When you have set crystals in all of the statues in the six palaces, the 'binding force' placed on the Valley of Death will be removed and you will be able to enter the great palace. There you must fight the last guardian. And you can obtain the Triforce only by defeating that guardian. There's nothing to fear. You are the one to get the Triforce. You are the beacon of hope for Hyrule.'

This explained Link's current situation, the symbol on his hand, and the purpose of the crystals to the young hero. With a great deal of resolve and courage, he pledged to Impa that he would find a way to restore the six crystals to the six palaces scattered across Hyrule and enter the Valley of Death to reach the Great Palace. After much toil, Link succeeded in restoring the crystals to their statues, breaking the barrier cast by the King over the Valley of Death. He finally reached the Great Palace, as described in the King's scroll, and faced his toughest challenge yet as he neared the end of his quest for the Triforce of Courage. Near the relic's resting place, the young hero came face to face with the mighty Thunderbird, one of the strongest guardians of the palace, though the beast ultimately fell to Link's blade. Just beyond the beast's chamber however, Link had to face his toughest adversary yet: his own shadow. After besting his dark shade, the hero was able to reclaim the Triforce of Courage. Uniting it with the other two restored the Triforce to its most powerful form and subsequently awakened the princess from her age-old slumber.

Trivia

 * A tomb known as the King's Tomb appears in the game and is generally considered to be the tomb of the ancient King of Hyrule that mastered the Triforce in its entirety. The tomb rests in the heart of the Graveyard to the southwest of the Harbor Town of Mido and can be easily spotted as a lone cross in the center of the graveyard.