The hero of 100 years ago and the one who 'defeated' Glen Baskerville. He is revealed to have been Gilbert's master 100 years ago, having taken in both him and Vincent. He has some sort of connection with Alice's memories. Jack looks like a grown-up Oz with a long plait. His personality is also similar; Like Oz, he does things at his own pace and is loud and cheerful. Oz and Gilbert meet him when they are taken to the Cheshire Cat's dimension. He is currently residing in Oz's body and can 'possess' Oz and speak through him. When in control, Jack also has full control of Alice's chain power. Jack was the third son of the Vessalius family who was, before the Tragedy of Sabrie, a third-rate noble family. Thus, with no expectations from his family, he acted quite freely: always smiling, joking and flirting with girls. Jack was also a self-proclaimed music box maker. His best friend at that time was Glen Baskerville. Jack crafted a pocket watch for him and Glen wrote the melody, titled "Lacie". The pocket watch's melody was said to be a song that Lacie always sang to herself. Later, Jack killed Glen because he started the Tragedy of Sablier (because he believed that without Lacie, there was no meaning to life) and tried to kill Jack. Although hailed as a hero for this act, Jack did not want to kill his best friend. In a later entry in Jack Vessalius's diary, he wrote: "I have killed my best friend. Please... Please do not call me a hero." He also shows true anger when Lottie suggested that he killed Glen to gain fame and glory. Jack reveals, through his speech when he first possesses Oz, that Glen is still living. Despite this, he says to the Baskervilles that if they wish to repeat the past, he will once again turn his body into a blade that will destroy the Death Gods. Jack's Seiyū is Daisuke Ono.