Ocarina of Time
Link obtains the Red Tunic (or Goron's Tunic) from the Goron leader Darunia's son. You can also purchase one from the shop in Goron City. This special article of clothing allows Link to survive in Death Mountain Crater, and enter the Fire Temple.
In Link's Awakening, the Red Tunic serves a completely differnt purpose than in Ocarina of Time. Firstly, it is not required to complete the game and is optional to aquire. You can only get this tunic in the DX version of the game in the Color Dungeon. After completeing the dungeon, the Great Fairy will give you an option to have more power or defense. The Red Tunic will grant you double attack power, while the Blue Tunic gives double defense.