The Great Deku Tree, also simply referred as the Great Deku Tree or Deku Tree, is the fatherly guardian of the forest who safeguards not only the dense land around him, but the small population of beings that live in his shadow. In Ocarina of Time, the Kokiri praise and worship the massive tree, sharing a home in the Kokiri Forest, while in The Wind Waker, these beings are the Koroks, timid wood creatures who live collaboratively with the talking tree in the Forest Haven.
Ikran's Lost OoT/Pokémon crossover[]

Link, Navi, Bulbasaur, Charmander, Squirtle, Sandshrew, Pikachu, Meowth and Scyther inside the Deku Tree
Of course, the Great Deku Tree served as a haven and a guardian over the Kokiri Forest, until one fateful night he became cursed as he refused to give the man of the desert the Kokiri Emerald. A day later, he stood there withering and summoned one of his children, Navi, and enlist her as Link's guardian fairy. She did just that, and they soon met Zelda II and her seven Pokémon. Once Link was able to find a Deku Shield and the Kokiri Sword to impress Mido, they finally reached the massive tree imploring them to save him from a deadly curse put onto him. He urged Navi, as well as the Pokémon Trainer, to guide the boy thru him and destroy the Queen Gohma inside. They were successful, and he congratulated Link as he demonstrated great courage; alas, they were too late. He then described the mysterious man of the desert laid the curse in exchange to one of the keys to the Sacred Realm. He then described how Hyrule was created by the 3 Golden Goddesses and left the Triforce behind as they parted, thus becoming the Sacred Realm. He said to Link to never let Ganondorf lay his hands on it, and they must see the Princess of Destiny for more intel. Unfortunately, that was when he passed on, as did the forest gradually.

The Sprout after he gave Link visions of his mom
The Great Deku Tree was seen again seven years later, after the heroes were successful on conquering the Forest Temple and saving Saria. Link wanted to pay his respects, and while the Trainer waited, she brushed upon a small stem. As she reached to brush away more soil, a large plant suddenly emerged, knocking her off her feet! He introduced himself as the Great Deku Sprout! And thru his roots, Link saw a vision of himself during the Hyrulean Civil War, as himself as a baby being taken by a dastard horse and a mother to the forest. Gravely injured, she pleaded for the Deku Tree to take in her son; sensing it was the Child of Destiny, he never hesitated. The Sprout was confident that Link and Zelda II can save Hyrule!
Tie a Yellow Ribbon Round the Deku Tree[]
The Tree's meadow was revisited as Link dreaded that if there isn't a yellow ribbon tied around the Deku Tree, he may end his life, feeling no one has appreciated his valiancy on saving Hyrule after the Imprisonment War. He actually saw a thousand yellow ribbons, showing that Link was more than welcome as a savior of Hyrule and the forest!