Kokiri

The Kokiri (コキリ, Kokiri) are forest-dwelling beings who live in the shadow of their patron deity, the Great Deku Tree. All Kokiri are green-tunic-wearing children, and have magical anti-aging characteristics. To date, they have only existed in the realms of Ocarina of Time and The Wind Waker, but are mentioned in passing in the game text of several games of the Zelda franchise.

Origins in Ocarina of Time
The Kokiri live under the leadership of Mido and the protection of the Great Deku Tree in the Kokiri Forest, deep within the Lost Woods region of Hyrule in Ocarina of Time. The Kokiri dress in green Kokiri Tunics, and have guardian and companion fairies who supervise them; these fairies seem to be gifts from the Great Deku Tree to the Kokiri. Every kokiri has a fairy.

Link was originally raised as a Kokiri, despite his Hylian heritage, based on a poignant move by his injured mother: she placed him in the care of the Great Deku Tree during the Hyrulean Civil War before her death in order to safeguard his life from the calamity beyond.

Lifestyle
The Kokiri were created by the Great Deku Tree and therefore, their homes are built not too far from him. It was said that the Kokiri die if they leave the forest. However, at the end of Ocarina of Time, the Kokiri are seen in Lon Lon Ranch along with other characters celebrating Ganondorf's defeat. Because of this, it is possible that the story is told only for general safety to prevent Kokiri to leave and be killed because of the monsters outside the Kokiri Forest.

The Kokiri appear predominantly in Ocarina of Time, but also make one appearance in The Wind Waker. The Wind Temple guardian and Wind Sage, Fado, is a Kokiri who looks and acts akin to his Ocarina of Time counterparts. Also, it has been confirmed by Eiji Aonuma that the Korok race is what the Kokiri became once they left the forest.

Leaving the Forest
Because the Kokiri are seen in Lon Lon Ranch at the end of Ocarina of Time, it is theorized that the story about their death when leaving the forest is of metaphorical nature, or at least one of general safety. If a Kokiri leaves the forest, they might be killed without the protection of the Great Deku Tree, and therefore eventually die if they do not return.

Eiji Aonuma stated "the Koroks were created as what the Kokiri became once they left the forest", thus it is possible that the Kokiri do not die once they leave the forest, but rather take on wooden bodies similar to that of the Koroks seen in The Wind Waker.

Trivia

 * The Japanese word for lumberjack (日本語) is pronounced "Kikori". This, combined with their green apparel of, leads some to believe that the Lumberjacks from A Link to the Past were in fact the inspiration for the Kokiri race.
 * The symbol of the Kokiri can be seen on the doors of the Forbidden Woods in The Wind Waker, and the doors of the Forest Temple in Twilight Princess. Crayk, the boss of the Temple of Courage in Phantom Hourglass, has also the Kokiri symbol on his shell repeated over several times.