Hyuga Ko

Hyuga Ko (日向コウ) is a unknown rank shinobi from the main house of Konohagakure's Hyuga clan.

Background
His birthday is a complete mystery. Most of Ko's early life is unknown except that he is reveal to be 9 years older than Naruto and Hinata. In the anime, Ko was Hinata's main caretaker for several years. It was his duty to watch over her whenever she was not at the Ninja Academy. He was showed to have a great care, and concern for Hinata's happiness and well being, and being disheartened whenever he saw her being sad. Kō often told her not to associate with Naruto, most likely because of Naruto's status as a jinchuriki. In fact, he accidentally mentioned the Nine Tailed Demon Fox in Hinata's presence, but when she questioned him about it, Ko told her not to worry about such things and to not talk to Naruto.

He then one day took her to see the Ninja Academy and told her that she will be going there soon. One day he came to Hinata's rescue after bullies were picking on her. He then took Hinata away from the Ninja Academy after she try to tell him that Naruto had save her.

During the Invasion of Konoha, Kō accompanied Hiashi in order to rescue Hinata after she was kidnapped by a pair of Kumogakure shinobi. He stopped on route to aide Tenten in defeating the mud wolves.

Personality
He has the same personality as everyone in the Hyuga clan. However like Natsu back then, Ko also treated Naruto poorly when he was a child. In later years he attended Naruto's Hokage ceremony.

Appearance
Ko has brown hair which is short, with backwards spikes. He has featureless white eyes, and his nose is broad and well defined. He wears the standard Konoha uniform inclusive of a flak jacket, and forehead protector that he wears like a bandanna. Casually, Kō wears the Hyuga clan's signature black kimono.

Abilities
While little is seen of his abilities, the fact that he was tasked with protecting the daughter of Hyuga clan's leader hints that Kō is a very skilled shinobi. Like all members of his clan, he possesses one of the three great dōjutsu, the Byakugan. These eyes grant him a near 360º of vision, and the capability to see through solid objects amongst other various abilities.

Invasion of Pain arc
During Pain's attack on the village, when Hinata initially attempted to aid Naruto in his fight against Pain, Ko having been tasked with protecting her during her father's absence called her back, claiming that she would only be a burden to Naruto. Later, he watched in horror with his Byakugan as Hinata went ahead regardless. He was unable to restrain her, due to a broken leg he had sustained when Pain had used his Shinra Tensei on the entire village.

Konoha History arc
In the anime, after the Invasion of Pain, he was seen in the infirmary tent with Hinata, who was tending his wounds.

Adventures at Sea arc
Ko was present at the meeting of the Hyuga clan convened by Hiashi. After hearing Hiashi declaration that Neji was to lead the clan's forces during the Fourth Shinobi War, he contested Hiashi's decision reminding him of how much Hinata had grown and that she was from the main house. Hiashi however, told him that it wasn't because he lacked faith in Hinata, but because she still lacked enough self-confidence to lead the shinobi during war.

Fourth Shinobi War arc
In the anime, Ko woke up from the Infinite Tsukuyomi alongside Hinata after Naruto and Sasuke released them. In the aftermath of the Fourth Shinobi War, Ko attends the mass funeral held in Konoha.

Naruto Shippuuden movie 6
Ko is seen next to Hinata, while everyone congratulates the Konoha 11 members victory for defeating the late Akatsuki members.

Quotes

 * It's nothing Hinata but you mustn't socialize with that boy.
 * (To Hyuga Hinata) "It would be my everlasting shame if anything were to happen to you while Hiashi and Hanabi were away".

Hyuga Hinata
He likes Hinata and cares about her a lot. Even trying to cheer her up when she gets sad. He also likes to hear how her processes as a ninja is going.

Trivia

 * Ko's name can mean anything from filial piety (孝) or body cavity (腔). But due the fact that most Hyuga clan members have light related names, it is most likely his name means "light" (光).
 * In the anime, Ko's appearance was changed. Instead of having light, spiky hair and a broad nose, he has a small nose and dark, straight hair. This made him look identical to the unnamed Hyūga that was with Sakura after Pain destroyed Konoha, hinting that the anime creators either conflated the two characters or, mistook them for one another.
 * Also in the anime where his back story is expanded, he is shown without a cursed seal, suggesting that he is from the Main House of the clan.
 * Studio Pierrot shows that Ko is 9 years older than Naruto and Hinata. Including that Kishimoto made him 170cms at the age of 17.

Voice Actors

 * Japanese : Yoji Ueda
 * English : Sam Reigel

all information on Hyuga Ko is from http://naruto.wikia.com/wiki/K%C5%8D_Hy%C5%ABga