Kyoya is a second-year student at Ouran High School, and vice-president of the host club. The "cool type" of the club, he is extremely intelligent and quite calculating, capable of manipulating events to serve any number of purposes. His family is primarily involved in hospital management and the medical industry with various other business interests as well, and supplies the school's medical staff and security (via its 100-member private police force). As the third son, Kyoya is unlikely to inherit leadership of the family's business unless he can surpass his older brothers' achievements to his father's satisfaction. This puts a lot of pressure on Kyoya, but he claims that he cannot think of a more interesting challenge. His family and the Suou family are rivals, so Kyoya initially befriended Tamaki because his father ordered him to for business reasons. However, as time passed, their friendship became genuine. Also, in the manga, he's shown to be sympathetic to his elder sister, Fuyumi, who was married; when their father saw her back in the house, he commented that married women shouldn't return home so readily.
Although Tamaki is the official leader of the club, Kyoya can easily influence Tamaki when he wants, and in a conflict between two of the other members of the club, they follow Kyoya's lead, causing Haruhi to refer to him privately as the "Shadow King." He was the only Host Club member to realize immediately that Haruhi was a girl, but kept the knowledge to himself in order to see what would happen; he often goes along with the Host Club's more eccentric antics, or even encourages them further, on the grounds that the results could be "interesting." Kyoya keeps track of various information about the students at Ouran Academy and is even in contact with Haruhi's father, who turns out to be the source from which Kyoya obtained Haruhi's photographs and information about her middle school popularity. He does not hesitate to turn a profit from the Host Club's popularity, even to the point of auctioning off items like Haruhi's pencil, and he keeps Haruhi in debt to the Host Club by finding various ways to add to it.
He claims to do nothing which does not profit him, and tells Haruhi that this is the only reason he is friends with Tamaki and involved with the Host Club, saying that there is "not one millimeter of similarity" between himself and Tamaki. This, however, appears to be a lie. Kyoya is altruistic in his own way, and often seems to act on Tamaki's behalf, most notably during the school festival in volume six of the manga. In his profile, Bisco Hatori notes that despite what he says, he and Tamaki are good friends.
Kyoya has low blood pressure and wakes up with a bad temper, earning him the nickname of "Low Blood Pressure Demon Lord". As such, he tends to sleep in until noon.
Something stated in the author's notes was that if the first volume of the manga had been 40 pages instead of 50 pages, Kyoya would have been dropped as a character all together. However, since the rest of the characters are the way they are, he is invaluable for maintaining order and offering explanations.
