Tōshirō Hitsugaya is very young by Soul Society standards. Born in the province of Jurin'an in the First District of West Rukongai, he became the youngest ever to graduate from the Shinigami Academy and subsequently rise to captain rank. Thus, many call him a "boy genius". He is short (because of his age) and has white hair, which tends to draw attention in the human world. He wears standard captain's garb, save for a green sash around his shoulders held together by a round clip, and sometimes walks around in his tabi. He is also one of two Shinigami that carry a Zanpakutō on their back, the other being Ichigo Kurosaki. Hitsugaya's short stature and the blade's length (about 120cm long) may explain the similar style. The sheath completely dissolves when he draws his sword.
Hitsugaya is generally mature and serious, in contrast to his free-spirited lieutenant, Rangiku Matsumoto. Despite their philosophical differences, he and Rangiku seem very close. Hitsugaya is shown to be easily annoyed by others goofing off or drawing unneeded attention to themselves, as he is when he leads a team of Shinigami into Ichigo Kurosaki's school. Hitsugaya hates anything that he deems childish and hates being described as something close to a child, an elementary school child for example, a further contrast to his appearance. This is shown more in the omake chapters of Bleach, such as the short comics in VJump and the sand castle contest chapter released along with chapter 238. He is also mistaken for a kid in several of the omake chapters, much to his annoyance. During the ending credits of the Sealed Sword Frenzy, he is in the human world and dressed in a young boy's school uniform, and Hinamori has to practically drag him out of hiding. He is overly protective of Momo Hinamori, due to the fact that they were old childhood friends. Hitsugaya dislikes summer and warm weather in general.
It is also known that Tōshirō's favorite food is sweet nattō, his Granny even used to send it to him into the division quarters. He does not like dried persimmons. Back in his childhood in West Rukongai, he was so skilled with spinning tops that he became the local undefeated champion. He works very hard, but his motive seems to be that if he finishes quickly, he can return to his afternoon nap. He believes in the saying "a child who sleeps will grow up", and hopes to grow quickly, a wish shared by his subordinates. Naturally, they do not voice this fact in front of him., for even regularly practicing this adage for so long, he didn't really grow up in height.
He is able to hide his presence well, on several occasions he manages to surprise Hinamori and Matsumoto with his sudden appearances, which leads them to complain about "sneaking up" upon them.
Hitsugaya gets easily annoyed when anyone (especially Momo Hinamori) refers to him by anything other than "Captain Hitsugaya". Hinamori tends to call him "Hitsugaya-kun" and both she and Ukitake occasionally use "Shiro-chan" (シロちゃん) — a nickname meaning "Whitey" (Snowy in the English manga) in reference to his hair — in both cases without any repercussion. In the Shinigami Golden Cup sketches (omakes found at the end of episodes of Bleach), Jūshirō Ukitake comically gives Hitsugaya candy and other food because "Jūshirō" and "Tōshirō" sound similar and because they both have white hair, making them both "Shiro-chan." The first character in Hitsugaya's given name, Tōshirō, means "winter," which is appropriate given his white hair and ice type Zanpakutō. Ichigo also calls Hitsugaya by his given name despite his many protests, much to his annoyance, and making him one of three captains Ichigo refers to in this manner (the others being Byakuya Kuchiki and Kenpachi Zaraki).
Hitsugaya's intuition is extremely sharp, and he is one of few captains to correctly suspect Gin Ichimaru of foul play, though he understandably did not yet suspect Sōsuke Aizen of the same.
During his duel with Gin Ichimaru in the anime, Ichimaru remarks that Hitsugaya is the embodiment of a heavenly guardian that would be reincarnated once in a while. This is attributed to his given name Tōshirō, which literally means "son of the winter lion (dragon/metaphor for magnificence)".
Even though he has relatively little amount of interaction with Ichigo, he helps in several potentially disastrous events, whenever ordered to by Yamamoto.
Hitsugaya as a kid back in Rukongai
Hitsugaya and Matsumoto arguing.
Hitsugaya comes from the province of Junrin'an in the 1st District of West Rukongai. There, he lived with his grandmother and Momo Hinamori. He also meets Rangiku, his future lieutenant for the first time there.
As a child, Hitsugaya was a bit of a brat who likes to eat watermelons and poke fun at Hinamori. She calls him "Shiro-chan" (Lil' Shiro in the English dub) and he retorts by calling her "Bed-wetter Momo." The two are close friends and Hitsugaya, despite being younger and much shorter than his friend, always feels that he needs to protect her.
When Hinamori left to become a Shinigami, he stayed behind despite knowing about his power. Her friends from next door were scared of him, although he does nothing to them, and does not visit or talk to him at all. "Granny" and Hinamori are the only ones in the district that weren't afraid of him. He was supposedly "cold as ice" or at least thought to be, and he often wondered if it was due to his appearance or attitude. After Momo had been in the academy for 5 years he began to notice how he hadn't grown an inch, while Hinamori's hair grew longer and she visited less often, seeming to have a goal in life now, and "Granny" was getting skinnier. It was there that he met Rangiku Matsumoto. She yelled at a shop keeper who was being rude to him and then at him for "lying there crying about it and not standing up like a man" although it was her who knocked him down with her large breasts in the first place, but he shook her off and ran away, probably in embarrassment. During that night he had a vivid dream of his Zanpakutō's spirit not only calling out to him (like in previous nights), but actually materializing in front of him in the form of a large dragon, and trying to tell him its name, which was unfortunately muffled by the strong winds. Soon after, Rangiku was able to track him down and woke him up, telling him that his Reiatsu was uncontrolled and leaking all over the place so it was causing Granny to freeze and get sicker, which may also explain why she got thinner. It was possible that if he stayed for too long while his reiatsu was still uncontrolled, he might have killed her. Rangiku told him to become a Shinigami in order to learn how to control his Reiatsu.
He is also a friend of Jidanbō Ikkanzaka, the West Gate Keeper, who taught him the "city rules."
With Hitsugaya's natural talent, he quickly entered the Shinigami Academy and graduated early despite his age. Hinamori continued to call him "Shiro-chan" out of habit and felt she needed to protect him. Because of a promise she had made, she only began to call him "Hitsugaya-kun" after he had achieved his Zanpakutō's Shikai and was recognized as a Shinigami. Highly capable and knowledgeable, he quickly became the youngest of the captains within the Gotei 13 in the entire history of Soul Society.