Kaname

A pureblood vampire who saved Yuki from an attack by another vampire when she was five years old. Kaname is the class president of the Night Class, both feared and respected by the other Night Class students.
While he is cold and authoritative towards his contemporaries in the Night Class, he is always kind and sweet to Yuki. He has shown that he cares for Yuki in a romantic sense ever since he saved her. He is also Yuki's fianceé and "so called" brother. Apparently, he allows Zero to live because he knows his death would sadden Yuki and because when he cannot protect Yuki, he knows that Zero will be there. However, he has another reason for keeping Zero. Kaname also asked Yuki to become a vampire and live with him for all eternity by his side, but manages to stop himself from biting her. He is both jealous and angry with Zero for biting Yuki and endangering her life. Later on, he bit Yuki in order to awaken her as a vampire and fed her his blood in order to revive her memories as a Kuran.
He also knows the pureblood who bit Zero, Shizuka Hiou, and later kills her before drinking her blood to gain power in order to protect Yuki, in spite of being a terrible taboo. It has been revealed in Chapter 38 that Haruka and Juri Kuran had a son, but his soul was killed by Rido Kuran and Kaname's soul was put into his body. Kaname was the ancestor of the Kuran Family thus resurrected by Rido from the grave, who became his 'master' making him unable to kill Rido. (Compare to the relationship between Shizuka Hiou and Zero). Juri and Haruka, Yuki's parents, raised Kaname as Yuki's brother, although Kaname never fully became 'their son'. Yuki and Kaname planned to marry as children, following the example of Juri and Haruka who were also brother and sister and married. At one point, Kaname allowed Zero to drink his blood to stave off insanity, preventing Zero from turning into a Level E for the time being, he does this for Yuki's sake and because Zero may be the only one able to kill Rido.
In Chapter 41, Kaname fears for Yuki's life when she refuses to leave the Academy for safety. Following Yuki's kiss, he doesn't give much of a reaction until she refers to him as "Onii-sama" as she used to call him 10 years ago. He then parts with Yuki to fulfill his own task. It is possible that this task is to kill the "monsters from the council".