The following contains spoilers for Tokyo Ghoul and Tokyo Ghoul :re.
Compared to the beginning of Tokyo Ghoul, Ken Kaneki has undergone significant transformations. Most people remember Kaneki's first major transformation, when, after being tormented, his hair became white and his personality changed dramatically. However, that is far from his only transformation.
Kaneki's perspective and physical appearance shift with each major event in the tragic hero's life. While he can be classified further, most fans agree that the patient Kaneki has six distinct personalities. It wouldn't be a leap to think of these Kens as completely different people, ranging from serene and gentle to nasty and crazy - and one of them is. Here is a list of all Kaneki forms, their characteristics, and where they fit in the series.
Kaneki 1 Is Shy and Bookish, with Black Hair
The first Kaneki is a shy, bookish college student who becomes a Half-Ghoul after a date goes horribly wrong. Luckily, he finds a place in the Ghoul-friendly coffee shop, Anteiku, where he works as a server and learns about the Ghoul community. As an idealist, this Kaneki is deeply troubled by an unjust world, and struggles to make sense of why Ghouls exist at all. Much later in the series, we learn that this Kaneki was withholding some pre-Ghoul trauma -- after losing his father, he was frequently abused by his mother, leading to severely low self-esteem. As a survival tactic, Black Hair Kaneki adopted the mindset of it being better to be hurt than to risk hurting others, though this lead to a weakness that he himself could hardly stand.
Kaneki 2 Is the Iconic Version, With White Hair
It's after being tortured that Kaneki undergoes his most iconic shift, accepting himself as a Ghoul as his hair turns white. There are a few theories as to why his hair suddenly changed color. A popular one is that it's due to Marie-Antoinette Syndrome, a real-life condition connecting white hair and trauma. Another involves his Ghoul awakening boosting his count of the fictional "RC cells." Regardless, the change was symbolic os Kaneki's personality shift. White Hair Kaneki rejects his past self, deciding strength is everything and all suffering is caused by one's lack of ability. Now cold, harsh and very powerful, Kaneki still wants to protect those close to him, but he pushes them away in doing so. As it turns out, this philosophy is his ultimate downfall. Anteiku is destroyed and Kaneki is cut down by Kishou Arima.
Kaneki 3 Is the Traumatized Centipede
Kaneki awakens as Centipede Kaneki, a powerful Ghoul metamorphosis enabled by cannibalization. In this state, Centipede Kaneki entirely loses control, babbling incomprehensibly, deliriously racing up walls and impaling adversaries with centipede tentacles. It is a manifestation of Kaneki's torture, with centipedes inserted into Jason's ear canal. When Kaneki's personalities gather in Tokyo Ghoul: re Chapter 141, this Kaneki was not present, implying that it may be an extension of White Kaneki rather than its own person. Prisoner #240 (who was present) is a muttering, insane identity constructed from Kaneki's horrific experiences.
Kaneki 4 Is Actually Haise Sasaki
Haise Sasaki isn't really Kaneki at all. After "dying" at Arima's hand, he is degraded to the nameless Prisoner #240 and revived as an amnesiac. Tortured and ashamed, he wants to forget everything that's happened to him. Captaining the Quinx Squad of the CCG, Sasaki is able to do just this, and he lives happily for a brief period as the kind, caring and somewhat awkward "den mother" of the Quinx. Of course, Kaneki's history comes knocking in the form of a hallucinated child Kaneki, who begs Sasaki not to erase the past. When Kaneki's memories return properly, he says, in one of the series' most memorable quotes, "Goodnight, Haise. I've had enough of dreaming."
Kaneki 5 Is the Darkest Personality, the Black Reaper
The Black Reaper is the darkest Kaneki in the series. Similar to White Kaneki, he is cruel, cold and merciless, recalling everything that has happened to him and refusing to accept Sasaki's momentary happiness. He remembers it all - the torture, the failure and even his childhood abuse. Similar to how White Kaneki deserts Anteiku, the Black Reaper deserts the Quinx squad. He even scolds Urie for not preventing Shirazu's death. He's definitely a lot bleaker than White Hair Kaneki, as he is explicitly suicidal. When he once again confronts the "White Reaper" Arima, he is fully prepared to die.
Kaneki 6 Is Tokyo Ghoul's Complex One-Eyed King
The One-Eyed King is perhaps Kaneki's most complex personality. Kaneki regains his will to life after his struggle with Arima and becomes the One-Eyed King. His former personalities merge to become a reformed, full Kaneki who understands what is vital and is ready to carry out Arima's desire. His hair turns white once more, indicating a favorable change in his character. It's clearly an improvement, but the sad hero's old flaws remain.
He takes on too much responsibility, and his life spirals out of control as a result of the stress. He eventually fails again, being killed by Juuzou Suzuya and transforming into the "Dragon" Kagune monster. Kaneki's visions inside Dragon help him make sense of himself and come to terms with the world in a more delicate way. He learns to rely on people and realizes that the world is neither right nor wrong; it simply is. The series concludes with this content, existentialist Kaneki.
