The Great Deku Tree is the guardian spirit of the forest of Hyrule and subsequently the protector and holder of the Spiritual Stone of the Forest, the Kokiri's Emerald. As an ancient, sentient being, he possesses vast knowledge about a great many things and is sensitive to the powers of fate. He is also the father and guardian of Saria's race, the Kokiri.

"...The Great Deku Tree is our father, the forest guardian, and he gave life to all of us Kokiri!"

The Great Deku Tree resides in the Kokiri Forest, very near to the Kokiri. However, the Kokiri don't see him often, and being summoned by the Great Deku Tree is considered a rare honour. To them, he is a father figure, wise and well respected for it. The Kokiri always adhere to whatever commands or facts he states, even if reason is not given for them.

The Great Deku Tree was also quite aware of Link's destiny. When Link's dying Hylian mother managed to escape into the Great Deku Tree's forbidden woods, he graciously took him into his care. Link grew up as a Kokiri, unbeknownst of his true heritage. Eventually Link began to have dreams of the future, which the Great Deku Tree was aware of but knew Link was then too young to do anything about them.

But when malevolent forces began to rise, the Great Deku Tree knew his time was near. Soon he was visited by a dangerous, dark man from the desert, demanding he hand over the Spiritual Stone of the Forest. The Great Deku Tree refused, and for this insult the evil man cursed the guardian of the forest and set the spider queen Gohma to slowly destroy him from the inside.

It was then that the Great Deku Tree called Navi to him and sent her to assist Link on his early quest. Although Link was able to defeat Queen Gohma and collect the Spiritual Stone, the corruption was too much for the Great Deku Tree. However, before he passed on, he was able to tell Link about Hyrule's destiny and direct his course to meet the Princess Zelda, who would surely help him in his quest.

To protect the Kokiri, the Great Deku Tree imposed a simple rule: that no Kokiri should leave the forest, or he or she would die. By doing this the Kokiri were kept sheltered from the outside world and all of the dangers present there, as well as living in relative ignorance with no worry of violent attacks.

However, this seemingly foolproof plan eventually backfires when, seven years after the forest guardian's death, the Kokiri Forest is invaded by Ganondorf's minions. Having never seriously practiced any offensive or even defensive fighting styles, the Kokiri were made to hide, instead of ridding their home of the corruption. Only when Link returns and destroys the evil is the Kokiri Forest saved.

After the Forest Temple is restored, the Deku Sprout, the reincarnation of the Deku Tree, appears. He tells Link about his true heritage as a Hylian and how he came to live as a Kokiri in the forest. Lastly, the Deku Sprout gives his final order to Link: to eliminate the curses in each of the temples and redeem the peace of Hyrule.

Deku is pronounced "DAY KOO", and originates from the Japanese word of the same romanji spelling (deku kanji: ). In Japanese, deku means "wooden figure", an accurate title as all deku-related items and beings are made up of or resemble wood.