Dark Link

Dark Link is one of the most well-known enemy characters in the Zelda universe, mostly due to his likeness and ability matching that of the protagonist, Link. It has been speculated that his popularity is so in part because he imitates almost every move Link makes, as if Link is fighting himself rather than a seperate entity; that is, Link and Dark Link are opposite in intentions, but perfectly matched in ability (as well as action).

In The Adventure of Link, Dark Link appears under the final boss in the game, he proves the most difficult opponent during Link's second quest to save Hyrule. He dodges most of the attacks that Link attempts, but he is vulnerable when he charges at Link.

Dark Link appears as a mini-boss in Ocarina of Time. He can be found in the Water Temple in a seemingly endless room. He mirrors most of Link's movements and attacks, usually defending himself in the process. To defeat him, Link must use the Megaton Hammer or the Biggoron Sword, or by using  his sword and while L/Z targeting him do a horizontal slash on the opposite side of his shield, which gives you an instant hit. Stocking up on magic potions and using Din's Fire is another option that makes the fight against Dark Link very easy. Once Link defeats his alter-ego, he is able to continue on to a room containing the Longshot.

In Four Swords Adventures, Dark Link yet again makes an apearance; this time by the name Shadow Link. He proves to be quite persistent, and is featured as a mini-boss several times before he is finally felled.

No one knows where Dark Link's origins are, but many speculations are out there. Some say that he is the ghost of a past warrior that is related to Link. Others think that, in a sort of dead-man-switch technique, Dark Link was created by Ganon himself as insurance, should he fall to Link's blade. Some say, just maybe, Dark Link was created out of Link's heroism. Because Link is the hero that he is, Dark Link arose due to complete Link's dark side. Everyone has a good and bad side to them, (Yin and Yang) thus, it is a widely accepted theory that Dark Link is the force that balances Link, and possibly keeps him alive. Regardless, it will be known in due time.

Dark Link also appears in one of the challenge scenarios in Super Smash Bros. Melee, where you must defeat him with Link.

Part of Dark Link's popularity is the sheer mystery behind him. Who is he? Why is he intent on combating Link? If, indeed, the before-mentioned theory is true, then, does Link have a dark side to him alone? Is he capable of doing no wrong?

Fierce Deity
Some People Belive That Oni (Fierce Deity) Link is Dark Link.

Bongo Bongo Theory
If the Timeline Theory is correct and Ocarina of Time Is the first game in the Timeline some people on a Forum Think that Bongo Bongos "Smoke" Form (That escaped from the Well) Only showed his True form when he flew through Link Thus Removing all Evil from Link and when Bongo Bongo was Destroyed Dark Link was Born. This is stopped by the Fact that Dark Link is in the Water Temple and you cannot Get to Bongo Bongo (Shadow Temple) until you've completed the Water Temple.

Descendent of the Twili
In Twilight Princess The Dark Magical Warriors who were descendents of the Twili look-like/Are Dark Link. Some people think that the Dark Links Are Just a representation of Evil but others think that Dark Links were the Real Descendents of the Twili which if true may mean Link was somehow related too the Dark Links and That Link and Midna are in Turn distantly Related.