Age: 13 at the start the of series(original), now 16-17(shippuden series)
Eye color: White
Hair color: Black
Height: 160 cm
Birthday: 3rd of July
Birth place: Konoha (Hidden Leaf)
Blood type: O
Debuted in Naruto Volume 4
Three words can effectively sum up Neji: calm, cooled and collected. Hailed as the prodigy of the Hyuuga clan, [an ancient family in the Hidden Leaf Village] Neji is a genius who has already mastered some of the most prestigious techniques the clan has to offer, and he is only a year older than Naruto. Neji carries the Advanced Bloodline of the "Byakugan" which is said to be one of the oldest advanced bloodline in the Hidden Leaf and the veritable ancestor of the Uchiha clan. Neji is discernible by his snow-white eyes [which are possessed by the entire clan]. So with this regal heir, Neji has become quite a haughty boy. He claims that destiny is the end all for everything and that we as humans cannot do anything. For such a talented young man that is one major downfall: his vindictive and bitter attitude towards people is something to be disliked. As we see from the series this mentality is passed down from generation to generation.
The Hyuuga family is split into two parts: the Main House and the Branch House. The reason they are separated is because the Main House is destined to hold the original blood of the Hyuuga and as such its heritage must be protected. The Branch house was created to protect the Main House at all costs thus resulting in the death and suffering of many a Branch House member. This slighted feeling that the Branch House possess is not unfounded. The Branch House members are put under a terrible curse at a young age. A curse seal Jutsu is cast on them and the symbol of "Bird in the Cage" is marked into their forehead which will stay there until they die. This brand isn't just to distinguish the Main House from the Branch House; it is in place so that the Main House can maintain a level of control to the lower members of the Hyuuga clan. A simple hand seal inflicts massive amount of agony into the mind of those who carry the mark and can quite easily kill them if need be. Neji belongs to the Branch House, and is marked like his fellow House members and his deceased father before him. This is where his hatred for the Main House and Hinata [his cousin] spawned.
When Neji was four years old, a Shinobi from the Cloud Country arrived in the Leaf Country to sign an alliance treaty because the warring factions had been at war for some time. All the while, it was the Hyuuga heirs birthday. The heir was Neji's cousin, Hinata. This would also be the day Neji had his seal carved into his head. Neji and Hinata's fathers were twins. Hinata's father Hiashi was the first-born of the pair and became a member of the Main House; Neji's father Hizashi was put into the Branch House. It was Hiashi who placed the seal onto Neji, making him a true Branch House member and he was sworn to protect the advanced blood for the rest of his life. A few days after the Shinobi from the Cloud Country had arrived, someone attempted to kidnap Hinata. Hiashi father quickly disposed of the assailant and revealed that it was the same Shinobi who had just signed the alliance agreement. It turned out that the Cloud Country was one of the many countries out to obtain the secrets of the Hyuuga and their Byakugan.
Enraged at the death of one of their leaders the Cloud Country demanded that Hiashi [the man who killed their Shinobi] be sacrificed. After much contemplation the Leaf Village succumbed to the Clouds demands. However, to keep the blood of the Main House alive, Hizashi's life was sacrificed and his corpse was sent to replace that of his brother [without letting Cloud know this]. That is the reason Neji hates the Main House. Without hesitation they sacrificed his fathers life for the betterment of the Main House. Neji directed all of his hatred of the Main House on Hinata who was their heir, albeit she was much weaker than Neji and completely incompetent as a Ninja to boot. A child with the potential to harness the ultimate power of the Hyuuga to its limit and at the same time is denied the heir is irony that Neji cannot comprehend. His goal is to surpass the Main House and to become so strong that nobody can defeat him. It is no doubt that with the Byakugan in his arsenal such a goal is entirely possible.
Neji's eyes allow him to do a lot of exceptional techniques but they also give him the comfort of having an absolute defense. One of his key techniques is the Heavenly Spin. Using the Byakugan to its potential, Neji can see 359 around his body and sense nearly all the attacks approaching him. Then, using his Hakkeshou, [the Chinese martial art of gentle fist fighting] Neji unlocks his chakra openings and decants large amounts of chakra to stop the incoming assault. He then uses his body to spin at high speeds to blast away anything within range. This technique has been only conquered by the Main House to date. For Neji to master this technique is extraordinary. Another example of Neji's attacks is the 64 hands of Hakke. This is a special technique that blocks every single chakra opening on the opponents body. This completely seals the chakra holes in the body [entrances in which chakra are released] rendering any Jutsus useless. The 64 hands of Hakke needs an extreme physical capability and for Neji to use it so facilely indubitably shows his brilliance as a Ninja.