Rauru

Rauru (ラウル) is an ancient Hylian and the Sage of Light in Ocarina of Time. He is one of the ancient Sages, and possibly the only remaining one. He lived in the Temple of Light, which is located in the Sacred Realm, for many centuries, guarding the Triforce.

Ocarina of Time
Link met Rauru after opening the Door of Time and drawing the Master Sword from the Pedestal of Time. Rauru recognized Link as the destined hero and kept him with him in the Sacred Realm for seven years, so that, in the safety of the Light Temple, he would become old enough to actually assume the role of hero. Rauru spoke with Link for the first time after those seven years, informing him of what had happened and what he was supposed to do as the hero. After instructing him to awaken the other Sages, Rauru gave him the Light Medallion.

Rauru contacted Link again when he had freed the other five Sages. He told Link to meet "someone" waiting at the Temple of Time before facing Ganondorf. This person turned out to be none other than the seventh Sage, Princess Zelda. Unfortunately, by revealing herself to Link, Ganondorf also was finally able to find her. Rauru then instructed Link to save Zelda and told him that he and the other Sages would aid him by providing entrance to Ganon's Castle. When Link defeated Ganon, Rauru led the other Sages when they used their powers to seal away Ganondorf.

Unlike the other Sages, Rauru was not seen at the ending of Ocarina of Time, possibly indicating that he stayed in the Light Temple.

The Wind Waker
While Rauru did not appear in The Wind Waker, one of the stained glass windows in Hyrule Castle's basement depicted him.

Kaepora Gaebora
It is believed by some that Kaepora Gaebora is the physical manifestation of Rauru outside of the Sacred Realm, which he uses to travel Hyrule. One argument for this theory is that a Gossip Stone refers to Kaepora Gaebora as "the reincarnation of an ancient Sage". Some also consider the quote of another Gossip Stone, that Kaepora Gaebora's "character is rather lighthearted", a reference to Rauru's position as the Sage of Light. However, Kaepora Gaebora himself has a quote that seems to contradict this theory. During the future part of Ocarina of Time, he can only be seen once, and at that time remarks that he "thought that the tales of a boy who could travel back and forth through time were merely a legend". If Kaepora Gaebora and Rauru really were one and same, Kaepora Gaebora should know that Link can travel though time. Although this could be an ancient prophecy which Rauru did not believe and he was merely expressing his surprise that it turned out to be true.

Some speculate that sages are able to 'pass on' their power and title as a sage. Proof of this is implied when Fado, as the final Kokiri, became the last Forest Sage, when the former forest sage was Saria. Also, the quote above might hint that a former Sage of Light was Kaepora, but over time, he gave his title and ability to Rauru. How one becomes a sage is unknown.

Trivia

 * Rauru, like several other characters from  Ocarina of Time was named after a town featured in The Adventure of Link.
 * The character Auru from Twilight Princess seems to be a reference to Rauru.