Volvagia

A legendary monster in Goron lore, Volvagia is the boss residing in the Fire Temple. The fierce, snake like dragon can only be killed with the legendary Megaton Hammer. Long dead, this dragon has been revived by Ganondorf. He plans on feeding the native Gorons to him in order to "make an example". If Link does not destroy Volvagia and free the Gorons, Hyrule will become a burning wasteland if the dragon escapes.

Strategy
This dragon is no pushover. On the battle field, there are pits of fire that Volvagia bursts out of. His head will pop out from one of the pits. Look for one pit that is spitting fire. That is a telltale sign that this pit is the one he will most likely come out from. Once Volvagia comes out, he would do one of two attacks. If you are far away, he will breath fire. If you are up close to him, he will try to slash you. You must get close to him and smack the Megaton Hammer on Volvagia's head. Once stunned, you can slash him with the Master Sword or hit him on the head again with the hammer. Eventually, he will leave his pit and attack you out on the field, flying through the air. He will either cause rocks to fall down at you (watch the shadows of the falling rocks to avoid them), or he will follow you and try to burn you. You can use your arrows at that point to fend Volvagia off. Try to catch him under the chin with the arrow shots.

After four smacks with the Megaton Hammer and four slashes with the Master Sword, the almighty dragon is defeated and the Gorons are saved. Watch as his body burns into a skeleton and his skull crashes to the ground. It will flew its jaw one last time and burn up, rewarding you with a Heart Container and a very pleased Darunia.

Trivia
Some specualtion surrounding the beast is that it has some kind of relation to Valoo, the guardian of the Rito in Wind Waker. This is due to the coloring of the two creatures, and that they both, presumably, reside at the same location. (Dragon Roost Island, where Valoo lives, and Death Mountain, where Volvagia lives, are considered to be the same thing.)

In the OoT manga, Volvagia was Link's pet, but Ganon cursed it like Great Deku Tree and Gohma.

Background
Volvagia was an ancient dragon that lived in the depths of the fiery Death Mountain. Long before Link was born, it was said that a legendary Goron destroyed Volvagia with the use of the Megaton Hammer. When The Legend of Zelda: Ocarina of Time's story occured, it was then that Ganondorf revived the devastating ferocious being to stop Link in his tracks and killajklfjanfnanfanfkajhim.