Zero is a tall young man with short straight silver hair, snowy-white skin and lavender eyes, the latter varying in shade from the manga to anime. Zero is a casual dresser and is usually wearing his school uniform incorrectly, with the vest and red tie exposed from under his black jacket. He also wears five silver earrings: three on his left ear cartilage (top) and two on his right (bottom). Zero bears a tattoo, the Hunter's Seal, on the left side of his neck, originally used to suppress his vampire side, and later used to tame him. He has grown taller as the series progresses.

Zero is considered to be attractive and handsome, by both Day and Night Class students.

Zero was born to a Vampire Hunter's family. Zero, along with his identical twin brother, Ichiru, and Kaito Takamiya, were trained as vampire hunters by Toga Yagari, who frequently looked after the twins when Zero's parents were out hunting. Yagari's fiancée, who was a doctor at Zero's school, was bitten by a Pureblood vampire and escaped custody. Although Zero defied orders to stay away, refusing that the doctor was dangerous, he was almost attacked due to her falling to a Level E state. Yagari shielded him, causing him to lose his eye. This was Zero's first lesson on the danger of seemingly innocent vampires. Yagari later tells the young Zero that he will never regret losing his eye to protect him and Ichiru.

Four years prior to the main events at the start of Vampire Knight, Zero and Ichiru found Shizuka Hio sitting in a tree. Zero immediately recognized her as a vampire and warned Ichiru to stay away. A few days later, Shizuka attacked his family. She bit Zero and killed his parents; Zero tried to warn Ichiru, but passed out not long after realizing that Ichiru had in fact betrayed his family, allow Shizuka to take revenge. He later would claim that he believed Ichiru to be dead, knowing the truth was far different.

After that attack, Zero was taken in by Kaien Cross. Yuki approached him carefully and cared for him despite him being cold and hostile towards her. Zero gradually grew affection for her, but kept it to himself due to her love for Kaname Kuran. Zero failed to reveal that he was going to turn into a vampire after Yuki said she was afraid of all other vampires. Over the next four years, the two become closer but not on a level they could truly call each other friends.

Zero is a vampire hunter who was chosen by Kaname to become a Pureblood killing machine. Zero possesses the standard abilities to sense vampires from a far distance, accelerated healing and in spite of being a vampire, is also able to wield anti-vampire weapons. Since he became a vampire, Zero is able to distinguish Purebloods from other vampires and has gained improved healing abilities. Kaname tells Zero that after he devours Ichiru's blood, he would become the world's strongest hunter. He then explains that since he has drank from Yuki's since she was a Pureblood, as well as Kaname and Shizuka's blood, it has made him the most powerful vampire hunter. After completing the fragment, along with Ichiru now being deceased, Bloody Rose has now become a part of his body, growing vines that can easily kill vampires, although it requires a high dosage of his blood to do so.