Great Deku Tree

Ocarina of Time
Guardian of the Kokiri and of their forest, the Great Deku Tree has been around since the beginning of Hyrule. He protects the Kokiri Emerald, one of the three Spiritual Stones.

The Great Deku was cursed by Ganondorf in Ocarina Of Time, and embarked Link on a quest to save Hyrule. He died shortly after telling Link to go save Princess Zelda. When he died, a seed fell from one of his higher branches to the ground. As an adult, Link goes back to find a new Deku Tree Sprout growing in front of the old Deku Tree.



The Legend of Zelda: The Wind Waker
The Deku Tree Sprout later grew up to be the God of the Earth, the Great Deku Tree, who turned the Kokiri into the Korok at the time of the Great Flood, and who helped Link, the Hero of the Winds, immensly in his quest.

One thing that set the Great Deku Tree of the Great Sea apart from his predecessor was that each year, the Great Deku Tree would send off some of the Koroks to plant trees all throughout the islands. This was done in the hope that, as the forests spread and the trees grew, they would consolidate the remaining land above the Great Sea, and allow some of the land lost during the Great Flood to be reclaimed from the depths.

It is very likely that the Forest Haven is the remains of the original Deku Tree; as it is likely that the "new" Forest Temple in Faron Woods is also the remains of the Deku Tree.

Manga
In the manga version, there is another talking tree known as the Baga Tree. He lives in the Lost Woods and has never beaten the Great Deku Tree once. The rumor that if you get lost in the woods, you turn into a skullkid is true, as that is what the Baga Tree does to them.