A Kokiri Forest fairy in The Legend of Zelda: Ocarina of Time, Navi is sent by The Great Deku Tree to awake Link and begin him on his journey. Navi accompanies this Link all throughout his adventure in Hyrule, constantly offering advice on where to go next. Navi can also offer Link information on an enemy he has targeted, such as its weaknesses, and movement patterns.
By the end of Link's journey, he has become The Hero of Time, bearer of the Triforce of Courage, with Navi's help. In his final fight with Ganondorf, Navi could not help because Ganondorf's power interfered with her. But when Ganondorf transformed into Ganon, she returns to assist Link in the final battle.
After the fight, Princess Zelda plays the Song of Time and sends Link and Navi back to his original time to recover lost years. When they return, Navi says her purpose is complete, and leaves Link. Link's search for her in the Lost Woods leads to the predicament that begins The Legend of Zelda: Majora's Mask. In that game, she is replaced by another fairy, Tatl.