Magician

The Magician is the character who, accordingly to the manual of, was close to the King who had ruled Hyrule and maintained peace with the Triforce. After the King died, his son became king and inherited everything he owned, except for the Triforce. The prince, who had been looking all over for the Triforce, was told by the magician that the King told Princess Zelda, the prince's sister, about the Triforce but she refused to tell him when he questioned her. The magician then angrily threatened to place her in an eternal sleep if she didn't tell him. After she refused the magician, he cast a spell on her despite the prince's attempts to stop him, and then seemingly dropped dead himself.

Identity
Although the true identity and nature of the magician is never revealed in the manual for The Adventure of Link, nor during the gameplay, Hyrule Historia has shed some light on his true nature. The book proposes two possibilities; due to his obsession with obtaining the Triforce, he is either a under the control or command of Ganon or possibly even an alter-ego of Ganon himself, much akin to Agahnim from. Like Agahnim, he too acted as an adviser to the king before revealing his true intentions. It is also suggested that casting the spell on Zelda caused the magician to die because it spent all of his power at once. In Valiant's The Legend of Zelda comic series, the identity of the wizard who placed the spell of eternal sleep is said to be Ganon.

The Adventure of Link manga
In Ran Maru's adaptation of the game, the Magician initially appears in the same backstory as in the manual, making a deal with the Prince and placing Zelda I in an eternal slumber. Unlike in the manual, the Magician escapes from the Prince after being wounded by his sword. Link soon encounters the Magician in the present day during his trek through Death Mountain. Here, the Magician is in charge of a cult comprised of Ganon's minions, inciting their mission to spill Link's blood on Ganon's ashes, in order to revive their master.

After the death of the werewolf swordsman, Ganpu, Link has a nightmare of Hyrule under the oppression of the Magician. Just as the Magician is about to bring harm to Zelda, Link strikes his mask and unveils the Prince. Immediately afterwards, Link wakes up. After Link crosses the sea to Eastern Hyrule, the Magician unleashes a storm that wrecks his ship. The Magician then launches an attack on the town of Darunia, but fails. A second attack is launched after the taming of the River Devil, leading to the death of the current Zelda. This attack is successful as the Magician now has blood needed to revive Ganon. By mistake, his minions have obtained Zelda's blood, rather than Link's, making the revival incomplete.

In the final volume, the Magician starts an all-out attack on Link, learning of the young hero completing his mission to return the crystals to the temples. After Link narrowly escapes Ganon, following the retreival of the Triforce of Courage, the Magician attempts to steal the Triforce in the guise of one of the nursemaids. Link sees through the disguise and cleaves off the Magician's mask. Zelda I recognizes him as both Ganon and the Prince. The Magician reveals that he has been attempting to get the Triforce for countless centuries, rapidly decaying before Ganon bursts through his body and snatches the Triforce. With his dying breath, the Magician reveals that Ganon is his alter-ego, and that his revival was necessary for him to continue living. He soon realizes that his own ambitions were his undoing and passes away, after apologizing to his sister.

Trivia

 * The magician bears an uncanny resemblance to Carock, the giant Wizzrobe boss of the Maze Island Palace.
 * As stated by Hyrule Historia, the magician also shares many similarities to Agahnim from A Link to the Past: both were close to the Royal Family of Hyrule but tricked them to further his own ends. Their pale blue skin and clawed hands are also extremely similar. The magician may have served as a prototype or concept for Agahnim.
 * The monster presiding over the wedding ceremony in the "Hitch in the Works" episode of The Legend of Zelda TV series looks similar to the Magician.