Toushirou Hitsugaya is very young by Soul Society standards. Born in Rukongai, he became the youngest ever to reach captain rank. Thus, he is called a "boy genius" or a "child prodigy" by many. Hitsugaya is very short with size comparable to Rukia Kuchiki's. He also has white hair (which tends to draw attention in the human world) and emerald eyes, which evokes his ability of controlling ice and water. He wears standard captain's clothing, save for a green sash around his shoulders, and sometimes walks around in his tabi.
Hitsugaya is generally mature and serious, in contrast to his free-spirited lieutenant, Rangiku Matsumoto. Despite their personality differences, he and Rangiku seem to be very close. Hitsugaya is shown to also be easily annoyed by others goofing off or drawing unneeded attention to themselves, as shown when he led 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. He is overly protective of Momo Hinamori, due to fact that they were old childhood friends. Fitting with the nature of his zanpakuto, Hitsugaya dislikes summer and warm weather in general.
A running gag is Hitsugaya getting annoyed when anyone refers to him by anything other than his title, Captain Hitsugaya. Hinamori has called him by "Toushirou," and both she and Ukitake have occasionally used "Lil' Shiro" (Shiro-chan) - a nickname meaning "Snowy" in reference to his hair - in both cases without repercussion, however. In the Shinigami Golden Picture Book sketches, Jushiro Ukitake comically gives Hitsugaya candy and other food because "Jushiro" and "Toushirou" sound similar and because they both have white hair, making them both "Shiro-chan." The first character in Hitsugaya's given name, Toushirou, means "winter," which is appropriate given his white hair and ice type zanpakuto. Ichigo also calls Hitsugaya by his given name, much to Hitsugaya's annoyance despite his protests, 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 didn't suspect Sosuke Aizen of the same.
During his duel with Gin Ichimaru, Ichimaru remarks that Hitsugaya is the embodiment of a heavenly guardian that would be reincarnated once in a few centuries. This is attributed to his given name, which is a homonym for a casual Japanese term meaning "amateur", possibly referring to Hitsugaya's young age and inexperience relative to the other captains of the Gotei 13.
"Sit upon the frosted heavens Hyorinmaru."