Dark Link

Dark Link, also known as Shadow Link, was a recurring villain throughout The Legend of Zelda. He is often thought as a doppelgänger of Link. He debuted in Zelda II: The Adventure of Link as the final boss of the game.

Characteristics
Dark Link appears in the form of Link's shadow. He mimics all of Link's moves. In his most recent appearance, The Legend of Zelda: Four Swords Adventures, he has a Joker-type personality and uses Megaton Hammers, bombs, and flame rods, among other weapons. He has the ability to warp between Hyrule and the Dark World as he wishes.

Dark Link was made to combat the Hero of Time being everything that Link is not and everything that he is at the same time. He holds the skills of the hero but instead of all things good, he is bad. He is filled with evil and a need to destroy the hero and the line of the hero. Dark Link in Zelda II: The Adventure of Link is the same person as the one in The Legend of Zelda: Ocarina of Time, but the Link is different. Unlike Dark Link, Link is not immortal and eventually dies. But every few hundred years a new Link in the bloodline of the hero of time is born and must eventually face off with Dark Link. In The Ocarina of Time, no matter what you do he kills you if you z-target. you must fight him normally and he won't counter your attacks.

He also has the ability to multiply himself and make himself look like Link.

Creation
During the Imprisoning War in which Ganondorf rose to power for the first time, Link stormed the Water Temple to destroy the source of the water drainage of Lake Hylia, Morpha. Link eventually reached a strange room, which was designed by Ganondorf to look like an island. Ganondorf's magic caused Link's shadow to rise from the floor, creating Dark Link.

Dark Link was bested in a sword duel with Link. Though, he wasn't killed.

Zelda II: The Adventure of Link
Dark Link's first appearances was in Zelda II as the final boss of the game. The forces of Ganon, striving to revive him, partially revived him in the form of Link's shadow. He was defeated by Link, who after the ordeal saved Princess Zelda.

The Legend of Zelda: Ocarina of Time
Dark Link appears as a Mini-Boss of the Water Temple. He can use some of the Link's sword attacks and is one of the hardest enemies in all the game.

The Legend of Zelda: Oracle of Ages
In The Legend of Zelda: Oracle of Ages, the game's main villain and final boss Veran summons multiple copies of Dark Link throughout the battle. These copies are significantly weaker than the real Link, and are mainly used by Veran as a distraction.

The Legend of Zelda: Four Swords Adventures
In Four Swords Adventures, Ganon uses Dark Link to deceive Link into drawing the Four Sword from it's pedestal, releasing Vaati the wind mage, who abducts the seven maidens and Zelda. Dark Link is a main antagonist in the game, a recurring mini-boss, and has a new trademark giggle.

He constantly duplicates himself constantly and alters himself to look like one of the four Links, requiring the same Link to defeat him.

Dark Link is killed at the end of the game by the effects of the Mirror.

The Legend of Zelda: Twilight Princess
Dark Link appears as a cameo appearance in Twilight Princess. 3 Dark Links symbolize the interlopers that broke into the Dark World in the vision to Link of the creation of Hyrule.

Super Smash Bros. Melee
Dark Link makes a cameo appearance in Super Smash Bros. Melee as the opponent in event match Link's Adventure.

Comics and Manga
In the manga version of The Legend of Zelda: Ocarina of Time, Dark Link makes one appearance. While Link is training with Impa in Kakariko Village, Dark Link appears from the well and attacks Link, only to be defeated.

In the manga of The Legend of Zelda: Four Swords Adventures, Shadow Link appears and is expanded upon. Here, he seems to attempt to tempt the real Links to evil and otherwise to sabotage their mission. His nature is explained as "The shadow version of Link from the Dark World".