Eldin, also known as the Fire Dragon, is a character from The Legend of Zelda: Skyward Sword. He is one of the Three Dragons who oversee The Surface. He is a large dragon Deity that watches over Eldin Volcano, as tasked by the goddess Hylia. Eldin resides in a cave at Eldin Volcano's summit and has power over the element of fire.
After Link defeats the parasite infecting Levias, he tells Link that the Three Dragons and himself each guard one part of the "Song of the Hero". While searching for these parts, Link travels to Eldin Volcano, where he is captured by Bokoblins and forced to regain all of his gear.
After regaining some of his items, Link travels to the Volcano Summit, where he finds the Master Sword and his remaining equipment. He then travels across a small lava lake to a room inhabited by Eldin, who teaches him his part of the "Song of the Hero".
According to the Gossip Stone found in the cavern east of the Earth Temple, Eldin is quite chatty; so much so that he will even speak of things "outside his own realm". As such, if Link returns to him after learning his part of the "Song of the Hero", he will talk about Eldin Volcano and the other two dragons.
Eldin is of the opinion that Faron is strong-willed, and warns Link to be careful in his dealings with her, lest he be eaten. Eldin speaks of a "legendary shield" that Lanayru treasures above all else. Eldin considers him to be wily, and warns that the trials he will present to those he sees as promising are not as easy as they appear.
"Eldin" is likely named after the goddess Din.