Hylia's Chosen Hero

Hylia's Chosen Hero, also known as the Knight of Hylia, is a hero chosen by the Goddess Hylia in an era shorly after the creation of the world by the Golden Goddesses, thousands of years prior to the events of Skyward Sword. Although only briefly mentioned in the game, Hylia's Chosen Hero plays a significant role in the Skyward Sword manga, where he is depicted as the earliest incarnation of Link. This has not been confirmed canonically. In the manga, he is clothed in Link's signature green garb, as well as a red cape.

Background
Little is known about Hylia's Chosen Hero's story except that he was born on the Surface during the Era of the Goddess Hylia. It is implied that he was born in a city that soon turned into Skyloft by the Goddess Hylia. According to legend, Her Grace made him her chosen hero and gave her Sailcloth to him.

The Battle Against Demise
Hylia's Chosen Hero fought with the Goddess Hylia during the war against the Demon King and somehow died, leaving the Hylia the only one left to protect the world against Demise.

Skyward Sword Manga
In the Skyward Sword manga by Akira Himekawa, Hylia's Chosen Hero is an incarnation of Link. He lives in a city in the world below the clouds known as the Land of Hylia.

Link becomes a Knight of Hylia, respected by the Hylian citizens and regarded as a hero. However, the hero is imprisoned for four years after his sword, Orville, is broken, and he is decieved by Lord Dagianis, who is killed four years later by Demise. After his death, the people free the Knight of Hylia from his prison. They say that he is the only one capable of saving the land from Demise's army of monsters, then give him his repaired sword and his clothes. The Knight of Hylia, Link, appears atop the castle, facing a crowd cheereing for him. Gazing at the sky, he says to himself that he will fight for the Goddess Hylia forever as long as she needs him. Ready to fight with his allies against Demise and his army, the Goddess Hylia suddenly appears in person, riding on an old Loftwing. The articulate Loftwing expresses his low opinion of the Hylians, saying that they are useless and didn't know the differences of deities and monsters. He could not believe that the hero who would ride him and face Demise could be among the people of the Surface. Link reveals himself as the Knight of Hylia and the hero whom they sought. He claims that, although humans may seem small in the eyes of the gods, there are those among them who possess great courage. Hylia acknowledges her knight's unmatched valiance and honor and proclaims him her chosen hero. She then allows him to wield her legendary weapon brought by the gods, the Master Sword.

Incarnation of Link
Hylia's Chosen Hero may himself be an incarnation of Link, as portrayed in the manga. In an interview, Eiji Aonuma stated the possibility of future games taking place before Skyward Sword in the Zelda Timeline. If this were to occur, Hylia's Chosen Hero would be a likely candidate for the next Link in the series (or the first, chronologically). This Link would be first to possess the Spirit of the Hero which would be passed down onto his descendants.

The Chosen Hero's descendant
Hylia's Chosen Hero is briefly mentioned during the events of Skyward Sword and it is hinted that Link is the descendant of the hero. Link in Skyward Sword therefore inherits the the hero's spirit and powers, making him the only one to defeat Demise.

Spirit of the Hero/The Chosen Hero Reborn
It was also hinted many times that Link is the living embodiment of Hylia's Chosen Hero. The spirit of the hero is most certainly Hylia's Chosen Hero's that was then transfered into his successor, as he is the chosen hero before Link thousands of years prior the events of Skyward Sword. As Link possesses the spirit of the hero, it makes him the hero's reincarnation, so he could continue fight for Hylia and her incarnations endlessly. Link is the person who possesses the hero's unbreakable spirit, who the Goddess Hylia needs to defeat Demise. However, just having Hylia's Chosen Hero's spirit wasn't enough; Link needed to awaken the spirit of the hero within himself.

Goddess Sword/Master Sword
It is probable that Hylia's Chosen Hero was also wielding the Goddess Sword during the Era of the Goddess Hylia, until one day, the hero managed to turn it into the Master Sword, as seen in the manga.