Age: 500+ ? (Appears 18)
Birthday: April 5
Sign: Aries
Blood Type: O
Height: 162 cm (5'4)
Weight: 51 kg (112 lbs.)
Hair: Brown
Eyes: Gold
Hobbies: Eating, fighting, being with Sanzou
Dislikes: Being alone, being hungry

Perpetually hungry, energetic and playful, Gokuu is the constant companion by Sanzou's side, viewing him as the 'sun' that his world revolves around. He is actually neither demon nor human, but is a heretic that was given birth by the Earth itself. He is very fast as well as strong, and uses his nyoibou [an extendable staff] to fight demons in battle. He accompanied Sanzou on his journey, and is often seen trading insults with Gojyo or fighting with him over food. The diadem that Gokuu wears on his head is actually a limiter to suppress his true form, the Seiten Taisei, or the Sage Equal to Heaven. When in this form, Gokuu is incredibly powerful and nearly unstoppable. He usually can't distinguish between friend or foe in this form, and often turns his attack toward his companions. Sanzou is capable of conjuring Gokuu's limiter in the event that it breaks.

He is also known as the monkey king.

Although Gokuu has a youthful appearance, he is actually over 500 years old. Previously, he was taken from where he dwelled on Earth into Heaven due to his potential danger. Shortly after his arrival, he was placed under the care of the god Konzen Douji, who he was drawn to because of his great beauty and golden hair that reminded Gokuu of the sun in the world below. Gokuu soon befriended the war prince Nataku as well as Konzen's friend Tenpou and his companion General Kenren.

Unfortunately, Gokuu became embroiled in the politics of Heaven. Due to the stress of certain events, Gokuu's limiter broke, causing him to revert to his true form. He killed a number of gods who tried to attack him, and his three friends Konzen, Tenpou, and Kenren, took him and fled. After the deaths of Gokuu's companions [the circumstances of which have yet to be revealed], his memories were sealed and he was imprisoned on Earth at the base of a mountain for his crimes against Heaven. Centuries later, Genjou Sanzou was drawn to the place that Gokuu was imprisoned by the sound of his 'voice.' The monk reached out to Gokuu, and the chains that bound him and the bars that confined him vanished. Since then, Gokuu has always been at Sanzou's side, not realizing that he has been reunited with the caretaker that he adored so long ago, as well as the two friends that he lost.
(Source: Saiyuuki Fansite, Saiyuuki Wikia)