Originally born as a human, his encounter with a female ghoul under the name of Kamishiro Rize forced him to undergo emergency surgery procedures after his assault by her. Cunning and manipulative, Rize uses her charms and Kaneki's attraction toward her as a means of getting her next "meal." After the attack, Kaneki is rushed to the hospital in a half-dead state with Rize. A doctor of the name Kanou, who secretly experiments with ghouls, humans, and half-ghouls, transplants what Kaneki believes to be a kidney into his body as a means of saving his life in the dire situation. Soon he learns that he had part of Rize's kagune transplanted into him, becoming the first of many human-ghoul experiments Kanou will conduct. Due to the unnatural abundance of RC Cells now present in his body because of Rize's kagune, Kaneki loses the ability to stomach human food, often getting sick or vomiting when ingesting any, and gains the powers of regeneration and kagune usage as a result. Because of his morals and attachment to humanity, Kaneki refuses to consume human beings as a means to sustain himself, even when the meat is obtained through non-violent means, rather he consumes large amounts of coffee, and, when absolutely necessary, will cannibalize other ghouls. Later, he joins with several ghouls, Banjou and Tsukiyama Shuu, in order to reduce the number of ghouls that cause havoc in the world to make the lives of humans better. Due to the nature of his ghoul mask and physical features, Kaneki earns himself the name "One-Eye" among the ghoul-community, and eventually "Centipede" when his kagune takes the form of one after he is put under immense stress, pressure, and anxiety. The CCG eventually dub him to be an SS-Rated ghoul. (Source: Tokyo Ghoul Wiki)

Spike Spiegel is a tall and lean 27-year-old bounty hunter born on Mars. The inspiration for Spike is found in martial artist Bruce Lee who uses the martial arts style of Jeet Kune Do as depicted in Session 8, "Waltz For Venus". He has fluffy, dark green hair (which is inspired by Yusaku Matsuda's) and reddish brown eyes, one of which is artificial and lighter than the other. He is usually dressed in a blue leisure suit, with a yellow shirt and Lupin III inspired boots. A flashback in Session 6 revealed it was his fully functioning right eye which was surgically replaced by the cybernetic one (although Spike himself may not have conscious recollection of the procedure since he claims to have lost his natural eye in an "accident"). One theory is that his natural eye may have been lost during the pre-series massacre in which he supposedly "died". The purpose of this cybernetic eye is never explicitly stated, though it apparently gives him exceptional hand-eye coordination - particularly with firearms (Spike's gun of choice is a Jericho 941, as seen throughout the series). In the first episode, when facing a bounty-head using Red Eye, Spike mocks him, calling his moves "too slow". At first, this seems like posturing on Spike's part, but even with his senses and reflexes accelerated to superhuman levels by the drug, the bounty cannot even touch Spike. A recurring device throughout the entire show is a closeup on Spike's fully-natural left eye before dissolving to a flashback of his life as part of the syndicate. As said by Spike himself in the last episode, his right eye "only sees the present" and his left eye "only sees the past." Spike often has a bent cigarette between his lips, sometimes despite rain or "No Smoking" signs.