- "Actually, when I see you, I am reminded of my son who left home long ago... Somehow, I feel as if I am once again racing with my son... I am afraid I may have tried too hard to outrun you. As old as I am, I am still a fast competitor. Just like when I raced my son... Please forgive my rudeness."
- — Deku Butler
The Deku Butler's Son is a character mentioned in The Legend of Zelda: Majora's Mask. He is never officially seen in the game; however, while it is not stated outright, it is implied that the withered tree in the caves beneath Clock Town may be his remains, and that the form Link takes while wearing the Deku Mask may be that of the Deku Butler's Son.
Prior to the events of Majora's Mask, the Deku Butler's Son lived at the Deku Palace with his father. He was said to enjoy racing his father through the maze-like Deku Shrine behind the palace. He is also said to have often used the Mask of Scents to find mushrooms in the forest. A long time prior to Link entering Termina, the Deku Butler's Son left the palace for reasons unexplained, and did not return.
The masks that cause Link to transform in Majora's Mask all seem to be inhabited by another character's soul. The Goron Mask houses the soul of Darmani, the Zora Mask houses the soul of Mikau, and the Fierce Deity's Mask presumably houses the soul of a great god. This leaves the Deku Mask with no real explanation as to how it helps Link transform.
When Link first enters Termina, the Skull Kid puts a curse on him, turning him into Deku Link. Soon after, Link stumbles across a twisted tree that resembles a Deku Scrub. Tatl remarks on how the tree "looks sad", as well as its physical resemblance to Link's current form. Later, when Link is to receive an item from the Deku Butler, the butler initiates a "race" in which he guides Link through a series of obstacles; if Link is able to keep up with him and reach the end of the shrine, he is given the Mask of Scents. Before Link leaves the shrine, the Deku Butler apologizes for moving too fast; he mentions that when he looks at Link, he is reminded of his son, whom he used to race, and that he therefore forgot to lower his pace. It is possible he is referring to Link's Deku form which he saw previously, as this is the most likely form to remind him of a Deku Scrub, though at the time he makes this statement Link may or may not be using that shape. During the game's end credits, the Deku Butler can be seen crying next to the twisted Deku-like tree seen in the caverns underneath Clock Town, which may imply he has finally found his long-lost son.
It is possible that when the Skull Kid cursed Link, he somehow infused him with the spirit of the Deku Butler's Son, which he may have somehow "extracted" from his body, leaving him a twisted tree somewhat reminiscent of his living form. When Link broke the curse with the "Song of Healing", he sealed the spirit of the Deku Butler's Son inside the mask. This theory is further supported by the Deku Scrub statue created by playing the "Elegy of Emptiness", which looks notably similar to the twisted tree and different from Link's Deku form; it has three leaves on the top instead of hair for example. The statues of Link's other forms, in two cases, resemble the physical forms of the spirits sealed inside the transformation masks, rather than resembling Link's forms when using the masks.
It is revealed that the Deku Princess was once attracted to the Deku Butler's Son, after Link was asked by the princess to change back in to his Deku form, and after the Butler compared Link's Deku form to him.