Din is one of the three Goddesses that created the land of Hyrule in The Legend of Zelda series, along with her sisters Farore and Nayru. She is the Goddess of Power, and using her "strong flaming arms", she "cultivated the land and created the red earth", thus forming the very bedrock that Hyrule sits upon.
Upon departing the land the three goddesses left behind a portion of their power in the sacred Triforce so as to keep the land in balance. Din's piece of the Triforce is the Triforce of Power, which is the part of the Triforce that Ganondorf holds.
Din is most often associated with the color red and the elements of fire and earth.
At the dawn of time, Din, along with Farore and Nayru, descended upon the chaos that was to become the land of Hyrule, each of them creating a different facet of the realm. According to The Legend of Zelda: Ocarina of Time, Din, "with her strong flaming arms" gave the earth its form. Upon departure, they created the Triforce, the essence of their power, and left it under Hylia's protection.
The Legend of Zelda: Ocarina of Time
In Ocarina of Time, Din appears in a flashback to the creation of Hyrule and the Triforce, told to Link by the Great Deku Tree. She is depicted as a golden figure surrounded by a red aura. She appears once again in the scene described by Princess Zelda upon her first meeting Link.
The spell Din's Fire is named after her.
The Era without a Hero
During The Era without a Hero, Din along with the others gods heard the pleas of the people of Hyrule who were faced by Ganon's onslaught of evil, instructed them to flee to Hyrule's mountaintops in order to escape the apocalypse they were about to unleash upon the land to halt Ganondorf's invasion by sealing him under The Great Sea along with the kingdom of Hyrule.
The Legend of Zelda: The Wind Waker
The Legend of Zelda: Twilight Princess
During the events of The Legend of Zelda: Twilight Princess, the light spirit Lanayru tell the tale of the creation of the kingdom of Hyrule by the three Goddesses and explain how him and the others light spirits were ordered to seal the power that the Dark Interlopers were using against Hyrule. The Goddesses are also said to have banished the said interlopers into the Twilight Realm.
The Legend of Zelda: A Link to the Past
In The Legend of Zelda: A Link to the Past Din is only mentioned in the game manual describing the creation of Hyrule and is said to be the "God of Power" before being renamed to a "deity" in the The Legend of Zelda: A Link to the Past & Four Swords version to fit the Ocarina of Time version.