Deku Butler's Son

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, but many player-made theories have arisen in regards to this issue.

Biography
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. Right before Link enters Termina, the Deku Butler's Son left the palace and has not been seen since.

Theory
The Masks that cause Link to transform in Majora's Mask all seem to have another character's soul that inhabits the mask. The Goron Mask houses the soul of Darmani, the Zora Mask houses the soul of Mikau, and the Fierce Deity Mask presumably houses the soul of a great god. This leaves the Deku Mask with no real explanation of how it helps Link transform. Some theories, however, help explain this.

When Link first enters Termina he is transformed into his Deku form. Soon after, he stumbles across a twisted tree that resembles a Deku. Tatl mentions that the tree looks sad, but nothing is really ever mentioned on the topic until Link beats the Woodfall Temple. After Link defeats Odolwa and saves the Deku Princess, he returns her to Deku Palace. Here he meets the Deku Butler who challenges Link to a race. After the race, the Deku Butler comments that Deku form Link resembles his son who has gone missing. Also by playing the "Elegy of Emptiness" the statue created looks similar to the tree beneath Clock Town further supporting the theory that the tree is the Deku Butler's Son.

During the ending credits of the game, the Deku Butler can be seen crying next to the Deku-like tree seen in the beginning of the game, which may imply he has finally found his long-lost son.

While non-canonical, in the manga, the Deku Princess notes the similarity between Deku Link and the Deku Butler's Son.

In the manga
It is revealed that the Deku Princess had a crush on the Deku Butler's Son.