- "You know, they say that the goddess gave the Sailcloth to her chosen hero long ago."
- — Zelda
Hylia's Chosen Hero is a character mentioned in the backstory of The Legend of Zelda: Skyward Sword. Little is known about the Hero except that the goddess Hylia gave him her Sailcloth at one point. It is likely he played some role in the war against Demise. Years later, Link takes up the legacy of Hylia's Chosen Hero during the events of Skyward Sword. Many relics and messages intended for Hylia's Chosen Hero are then utilized by Link.
The Skyward Sword manga gives more detail into the hero's backstory revealing him to be an incarnation of Link.
Somehow, Hylia's Chosen Hero heard word of an oncoming disaster and tried to warn the people of Hyrule about it. However he was framed and imprisoned. Four years later when the demons of Demise appeared, the people of Hyrule released the hero and asked him to help them fight. Rather than holding a grudge over his imprisonment, Link agreed to forgive the people and fight for Hyrule.
Some time afterwards, Hylia appeared on a Crimson Loftwing wielding the Master Sword. She gifted it upon the hero and asked him to assist her in sending Skyloft into The Sky. The hero believes he is not worthy to wield the sword but Hylia assures him that his suffering and love for Hyrule are the traits that are most important. He then reforges the sword knowing this fact and uses it to battle the hordes of Demise.
Eventually he comes face to face with Demise himself and does battle with the demon while riding the Crimson Loftwings. Then, the Three Dragons appeared and began sending the Skyloft into the sky. The hero assists using the power of the Master Sword but is unable to join the rest of his race. Injured from the battle, he dies in Hylia's arms. His bravery and courage prompt Hylia to reincarnate as a hylian so she can see be with his successor.
According to the Skyward Sword prologue, it was Hylia herself who used the Master Sword to battle Demise and send Skyloft into the heavens.
Hylia's Chosen Hero is Link from Skyward Sword
It is possible there was no original Hylia's Chosen Hero and the Hero spoken about in Legend is really Link, having travelled back in time to finish the battle of Demise. However, given that knowledge of the hero is present in Skyloft and the era Link travelled back to was a time after Skyward took to the Sky, it seems unlikely for this to be the case.