Volvagia

A legendary, snake-like dragon in Goron lore, Subterranean Lava Dragon: Volvagia is the boss residing in the Fire Temple. 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. By the time of Ocarina of Time, Ganondorf had revived the fierce creature to secure the corrupted Fire Temple from intrusion and, by feeding the native Gorons to Volvagia, to "make an example" to other people that might revolt against him. Incited by Darunia's son, Link set on to destroy Volvagia or else, if the dragon escaped from the temple, Hyrule would become a burning wasteland. In the game, Volvagia is referred to as "it", with a single instance in which it's gender is specified as male.

Barba
Volvagia bears a remarkable resemblance to Barba, a dragon boss in The Adventure of Link. Not only in appearance, but in name as well. Volvagia's Japanese name is "Varubajia" and Barba's "Barubajia". In written Japanese, the "V" and the "B" are the same letter.

Strategy
The battle is alot like "Whack-a-Mole" because there are nine holes, you have to whack the dragon when it comes out, and you have to use a hammer. 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, which 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 breathe fire. If you are up close to him, he will try to slash you. You must get close to him and strike Volvagia's head with the Megaton Hammer. 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 or you can go to the edge of the battle stage and hang there while the rocks fall down. Try to pierce 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 move its jaw one last time and burn up, rewarding you with a Heart Container and a very pleased Darunia.

In the Manga
In the The Legend of Zelda: Ocarina of Time Manga, Volvagia is a dragon that Link bought as a young child. When he returned 7 years later, Volvagia was corrupted by Ganondorf, requiring Link, begrudgingly, to kill it. Volvagia is also able to talk in the manga, albeit only the word 'Link'. Before his dying breath a single tear drops from Volvagia's eye and he sadly utters "L-L-Link"