The Three Dragons are a group from The Legend of Zelda: Skyward Sword. They are dragons who oversee The Surface, whose provinces—Faron Woods, Eldin Volcano, and Lanayru Desert—are named after each dragon, respectively. Faron has power over water, Eldin has power over fire, and Lanayru has power over lightning.
During the events of the game, Link is told by Levias that he must learn the "Song of the Hero" in order to obtain the Triforce. Levias knows part of the song, but the Three Dragons possess the knowledge of the rest, and Link must track down each one individually to learn their special part. Once he does this, he will be led to the Triforce.
Interestingly, they share their names with three of the Light Spirits (Faron, Eldin, and Lanayru) from The Legend of Zelda: Twilight Princess.