Triforce

The Triforce, also known as the Golden Power or the Power of Gold, is a golden, sacred relic that appears in many of The Legend of Zelda games. It was created by the three Golden Goddesses, Din, Nayru, and Farore, after they had created Hyrule. The Triforce is made up of three equilateral triangles, which are joined (with an inverted empty triangle in the middle) to form a large equilateral triangle.

Summary
The three pieces of the Triforce are distinctively known as the Triforce of Power, the Triforce of Wisdom, and the Triforce of Courage, and they each represent a unique characteristic. In many of the games, Ganon is associated with the Triforce of Power, Princess Zelda with the Triforce of Wisdom, and Link with the Triforce of Courage.

The Triforce represents the essence of the three goddesses, and grants godlike power to the person with the Triforce. As a result, throughout the the history of Hyrule, many have searched for the Triforce and have even waged war over it. At times, the three triangles of the Triforce have been split into smaller pieces and scattered due to fear of its misuse.

If an unworthy person attempts to claim the whole Triforce, its three parts separate, and the person only keeps the part that they believe in the most. The remaining two pieces each reside in two other chosen people, who can be identified by a triangular mark on the back of their hand. If the three pieces of the Triforce draw near, they resonate and attempt to reunify into a single Triforce. To unlock the full power of the Triforce, the person must demonstrate a balance of power, wisdom, and courage through a series of trials and have the complete Triforce in possession.

The Triforce has demonstrated some degree of sentience on occasion, and rarely communicates telepathically with a voice that refers to itself as the Essence of the Triforce.

The Legend of Zelda
The Triforce first appears in The Legend of Zelda, though it is only individually represented by the Triforce of Power and Triforce of Wisdom. The complete Triforce does not appear, and the manual describes both Triforce pieces as "golden triangles" (the "tri" prefix of Triforce could be derived from its triangular shape).

Zelda II: The Adventure of Link
Zelda II: The Adventure of Link is the first game to feature the whole Triforce due the debut appearance of the third piece, the Triforce of Courage.

In an era prior to the game's events, the King of Hyrule used the Triforce to maintain peace throughout Hyrule. He eventually died, and his heir, the prince, could only inherit part of the Triforce. The king had told a secret about the Triforce to only the prince's younger sister, Princess Zelda. She refused to tell the secret to the prince or to the magician, and the latter put her under a spell of eternal slumber.

One day, Impa showed a scroll to Link that explains the secret for uniting the Triforce. It reveals that both the Triforce of Power and of Wisdom remained in the Kingdom of Hyrule but the third piece, the Triforce of Courage, was hidden away. It further states that the Triforce must only be used by someone with no evil intent and an inborn special attribute. A triangular crest mark would appear on the back of a person worthy of possessing the Triforce. Link goes on an adventure to retrieve the Triforce of Courage from the Great Palace.

While the Triforce has a key role in the story, but its only in-game appearance is in the ending of Zelda II: The Adventure of Link. After getting the Triforce of Courage, Link uses the completed Triforce to awaken Princess Zelda from her slumber.

The Legend of Zelda: A Link to the Past
Ganon is sealed away by the seven sages in the Sacred Realm. Ganon, conquering it as the Dark World, possesses the Triforce and aims to conquer the Light World through his alter ego, Agahnim. However, he is defeated by Link. Link touches it and undoes the damage Ganon has done.

The Legend of Zelda: Ocarina of Time
In The Legend of Zelda: Ocarina of Time, Ganondorf touches it, and it splits apart. All that remains in him is the Triforce of Power, while the Triforce of Wisdom resides within Princess Zelda and the Triforce of Courage within Link, a boy who will become the Hero of Time. Ganondorf is eventually defeated and sealed away.

The Legend of Zelda: Oracle of Seasons/Ages
Link, who has the qualities of a hero, is bestowed with a set of trials by the Triforce. Once both are completed, the Triforce ascends into the sky, transforms into birds, and flies away, split.

The Legend of Zelda: The Wind Waker
The Hero of Time returns to his original era, and the Triforce of Courage splits into eight fragments and scatters. Later, Ganon revives, and Hyrule is sunk under the Great Sea. The Triforce is united. In the ending it is revealed that it first grants the wish of those who lay hands on it, but only the first person to touch it will have their wish granted. Daphnes Nohansen Hyrule wishes for Ganondorf to be submerged with Hyrule under the Great Sea. The Triforce vanishes, its whereabouts unknown.

The Legend of Zelda: Twilight Princess
Three individuals chosen by fate come to possess the three pieces of the Triforce. It dwells within one possessing the necessary qualities, bringing forth various powers. Ganondorf seeks its complete form but loses to Link, and his mark fades.

The Legend of Zelda: Skyward Sword
To eliminate the source of evil, Zelda and the hero gain the capability to wield the Triforce. They wish for the elimination of Demise.

The Legend of Zelda: A Link Between Worlds
The Triforce is desired by Lorule, after their own Triforce was destroyed. The hero and Princess Zelda touch Hyrule's Triforce, wishing for Lorule's to return.

Trivia

 * In the original The Legend of Zelda, the pieces of the Triforce were originally meant to be computer chips allowing Link to travel between the past and future.