The Deku are a species of sentient plant-life that reside in and around Mido's Swamp and Lake Saria near the Lost Woods in the Kokiri area, which they feel a draw to. They have green thumbs and tend to spread life and vegetation anywhere they go. They have a royal family, and technically reside in an underground monarchy known as the Deku Kingdom. They actually have a sophisticated education system, and all Deku are schooled in the ways of botany, mathematics, combat, and business.

They worship skull totems as a reminder of life and death, and offer reverence and fear to Skull Kids in possession of Skull Masks. Deku vary wildly in size, being plants. They can extend thick, flexible vines from both sides of their bodies to perfectly emulate arms, but do not have any naturally. They cannot swim, but instead are so light they may hop on top of water to stay afloat, and can even stand on lily pads if not weighed down a lot. They are also able to force large, rotating flowers to bloom atop their heads, allowing for gliding short distances and riding rising heat sources. From their muzzle-like mouths, they can fire various types of nuts and seeds. These features make Deku very versatile, even for their small size.

Deku gain nutrients from the ground. They can make small, temporary nests to soak their roots and revitalize themselves. They do not need to eat, though some have a fondness for the nuts and seeds they usually use as ammunition. They appear to be small wooden shrubs (though some can get very tall), with plant life making up the "hair" and "clothing" covering a Deku's body, and possess long, hollow snouts. They have a severe aversion to fire, as they are living wood and plant.