The Master Sword

"But then, when all hope had died, and the hour of doom seemed at hand... a young boy clothed in green appeared as if from nowhere. Wielding the blade of evil's bane, he sealed the dark one away and gave the land light."

- The Legend of Zelda: The Wind Waker

The Master Sword is typically the most powerful weapon in a Zelda game for general usage; with the exception of the Biggoron Sword and the upgrades in A Link to the Past. The master sword will usually have a power level of two or three unlike the starting sword. The sword is said to be forged many years before the Rise and Fall of Ganondorf, although it's exact origins, and makers are unknown.

The Legend of Zelda and The Adventure of Link
The Master Sword was belived not to appear in these games; however, according to Nintendo's official Zelda site, the Master Sword is listed as having appeared in The Legend of Zelda and The Adventure of Link, which was originally called the Magical Sword.

A Link to the Past
This was the game when The Master Sword properly was called that. The Master Sword here is the legendary blade that rests in the Lost Woods of northwestern Hyrule in a pedestal with ancient Hylian inscribed on it. The ancient text says the hero with all three Pendants will wield it on cataclysm's eve, reading: "The Hero's triumph on Cataclysm's Eve wins three Symbols of Virtue. The Master Sword he shall then receive, keeping the knights line true." This sword has the power to emit a beam from its blade to attack enemies from a distance. This happens only when Links health is completely full. It is the second sword acquired in the game, and the third and fourth swords are more powerful versions of the Master Sword. The Master Sword is also called "the Blade of Evil's Bane", and has the power to repel evil magic. A Link to the Past was also the first Zelda game to feature the Master Sword.

Ocarina of Time
This legendary blade resides in the Temple of Time. To gain the Sword, Link must collect the three Spiritual Stones, and use the Ocarina of Time to open the chamber where it is sealed. The Master Sword is the final key to the sacred realm that holds the Triforce, and only the one worthy of the title of the Hero of Time can draw the Master Sword. In both Ocarina and the Wind Waker, the Master Sword locks away evil from Hyrule. When removed from it's resting place, its prime purpose becomes to help attack and reseal evil and restore peace to the world. When Link pulls the Master Sword out of it's pedestal, he travels seven years into the future. He can also return to the past by plunging the sword back. In the end of the game, the Master Sword is used by Link to defeat Ganondorf and seal him into the Evil Realm.

The Wind Waker
The Master Sword is predominately referred to as the Blade of Evil's Bane in the Wind Waker legends and rests in a hidden chamber in Hyrule Castle, deep beneath the waves of the Great Sea. The Master Sword's use as a key to lock evil away is broken when a young Link unknowingly draws the blade under the direction of the King Of Red Lions. He unwittingly awakens Ganondorf´s army from their ancient slumber. Later, Link learns that the Master Sword (After Ganondorf killed Fado and Laruto, the last sages of the sacred realm that remain after the great flood) has lost its power to repel evil and Link must awaken two new sages in order to regain that power. Those sages are apparently there in order to pray for the Master Sword and the hero who wields it, and keep it glowing with the power to repel evil.

Twilight Princess
The Master Sword within Twilight Princess is located deep within the Faron Woods in the Sacred Grove (the ruins of the Temple of Time). The blade is said to have once be held by the Legendary Hero. It is the one relic that allowed Link to break the curse that Zant places on him after the end of Lakebed Temple and return to his human form. Link then draws the blade from its pedestal, and Midna proclaims that the sword chose Link to become it's new master.

The Master Sword in this game also allowed Link access to other numerous hidden temples later in the game (such as the Temple of Time). The sword's initial locations marks a link between A Link to the Past and Ocarina of Time, as it resides in the Temple's ruins, a place that is notably similar to the sword's resting place in A Link To The Past.

The sword is (in comparison with the shield and the overall height of Link) considerably bigger than in the other 3D releases. Regardless, the general design is consistent throughout them all.

Light-Infused Master Sword
In the Palace of Twilight, Link fuses the Master Sword with the power of the Sols. This Light-Infused Master Sword light sword enables Link to defeat most Twilight Monsters in a single hit. The sword is also capable of clearing away the dark fog which causes Link to revert back to wolf form. This upgrade is only usable while in the Twilight Realm.

Midna notes that the Sols' light being transfered to the Master Sword is the work of the gods of the Twilight Realm, and that they, too, are on Link's side.