Great Deku Tree
Ocarina of Time
In Ocarina of Time, the Great Deku Tree is in charge of watching over Link and the other Kokiri children in the Kokiri Forest. He watches over the Kokiri and is the guardian of the Kokiri Forest. He is considered responsible and wise. This is evidenced by the fact that Link's Mother trusted the Great Deku Tree to watch over Link during the wars that dominated when she was alive. At the beginning of Ocarina of Time, the Great Deku Tree orders Navi to bring Link over to him. He assigns a Fairy for each Kokiri in the forest, Navi being Link's companion throughout the game. The Great Deku Tree protects each of the Kokiri and saves them from the outside world of Hyrule and its horrors. Unfortunately, his death later allows monsters to sweep in and infest the once peaceful forest.
After being cursed by Ganondorf, the Great Deku Tree sends Navi to summon Link. When the two return, he informs Link of the curse and requests that he go enter his mouth in an attempt to eliminate the curse and "demonstrate his courage". Link successfully defeats the evil, Queen Gohma, dwelling inside the tree. 
The Great Deku Tree then tells the tale of how Hyrule came to be. He explains the story of the Golden Goddesses. He then gives Link the Kokiri's Emerald. However, it is too late. The curse has taken its toll, killing the Great Deku Tree. Some of his last words advise Link to go to Hyrule Castle to meet the Princess of Destiny" which leads to the events of the game.
After Link wakes up from his seven year slumber, he discovers that the Kokiri Forest is now infested with monsters. The Kokiri say this started happening after the death of the Great Deku Tree. When Link completes the Forest Temple, Link is transported back to the Kokiri Forest where he watches the Deku Tree Sprout grow in front of the dead Great Deku Tree. It is speculated that the Deku Tree Sprout is in fact the Great Deku Tree from The Wind Waker.
The Wind Waker
The Great Deku Tree is first seen covered in red and green ChuChus. After removing them, Link meets the Koroks. The Great Deku Tree sends Link to find Makar, the smallest Korok, who has been blown into the Forbidden Woods. He also gives Link the Deku Leaf. Link must use Baba Buds to get to the top of the Deku Tree and obtain the Deku Leaf.
After Link completes the third dungeon of the game, the Great Deku Tree answers his questions about Koroks. He also says that the Forest Water in Forest Haven is special and marks the places of Withered Forest Trees on the Sea Chart.
He is also seen as a caretaker here. He is furious and deeply concerned about Makar's disappearance into the Forbidden Woods. This shows that the Great Deku Tree cares about Korok underlings and seeks to protect them at all times.
Breath of the Wild
The Deku Tree makes an appearance in the Nintendo Land Plaza.
"This is a faithful re-creation of the great forest guardian, the Deku Tree. Are you feeling exhausted? How would you like to kick back and take a rest under the canopy of the Deku Tree? No, that wouldn't be terrifying at all."
- ↑ "In the vast, deep forest of Hyrule... Long have I served as the guardian spirit... I am known as the Deku Tree..." — Great Deku Tree, Ocarina of Time.
- ↑ "The children of the forest, the Kokiri, live here with me. Each Kokiri has his or her own guardian fairy." — Great Deku Tree, Ocarina of Time.
- ↑ "Oh, you have a fairy now?! That's great, Link! What? You've been called by the Great Deku Tree? What an honor! He may give you a special gift! Tee hee! That's because the Great Deku Tree is our father, the forest guardian, and he gave life to all of us Kokiri!" — Kokiri, Ocarina of Time.
- ↑ "Oh, Navi the fairy... Listen to my words, the words of the Deku Tree... Dost thou sense it? The climate of evil descending upon this realm... Malevolent forces even now are mustering to attack our land of Hyrule... For so long, the Kokiri Forest, the source of life, has stood as a barrier, deterring outsiders and maintaining the order of the world... But...before this tremendous evil power, even my power is as nothing... It seems the time has come for the boy without a fairy to begin his journey... The youth whose destiny it is to lead Hyrule to the path of justice and truth... Navi...go now! Find our young friend and guide him to me... I do not have much time left. Fly, Navi, fly! The fate of the forest, nay, the world, depends upon thee!" — Great Deku Tree, Ocarina of Time.
- ↑ "I have been cursed... I need you to break the curse with your wisdom and courage. Dost thou have courage enough to undertake this task? Yes No" — Great Deku Tree, Ocarina of Time.
- ↑ "Now...listen carefully... A wicked man of the desert cast this dreadful curse upon me..." — Great Deku Tree, Ocarina of Time.
- ↑ "This evil man ceaselessly uses his vile, sorcerous powers in his search for the Sacred Realm that is connected to Hyrule... For it is in that Sacred Realm that one will find the divine relic, the Triforce, which contains the essence of the gods..." — Great Deku Tree, Ocarina of Time.
- ↑ "Link... Go now to Hyrule Castle... There, thou will surely meet the Princess of Destiny... Take this stone with you. The stone that man wanted so much, that he cast the curse on me..." — Great Deku Tree, Ocarina of Time.
- ↑ "Thou must never allow the desert man in black armor to lay his hands on the sacred Triforce... Thou must never suffer that man, with his evil heart, to enter the Sacred Realm of legend... That evil man who cast the death curse upon me and sapped my power... Because of that curse, my end is nigh... Though your valiant efforts to break the curse were successful, I was doomed before you started... Yes, I will pass away soon... But do not grieve for me... I have been able to tell you of these important matters... This is Hyrule's final hope..." — Great Deku Tree, Ocarina of Time.
- ↑ "The future depends upon thee, Link... Thou art courageous... Navi the fairy... Help Link to carry out my will..." — Great Deku Tree, Ocarina of Time.
- ↑ "I entreat ye... Navi..." — Great Deku Tree, Ocarina of Time.
- ↑ " Good...bye..." — Great Deku Tree, Ocarina of Time.