Birthday: December 26
Age: 15
Gender: Male
Height: 164 cm (5'5")
Blood Type: O

The main character of the story. A 15-year-old boy with blond hair and green eyes from the prestigious Vessalius family, whose father is the reigning lord. His mother was killed by the Nightray family, but despite this, he retains a bright, optimistic, and energetic personality. The story of Pandora Hearts starts when Oz turns fifteen. During the ceremony to celebrate this reaching of adulthood, he was dragged into the Abyss for the sin of "existing." There he meets the chain named Alice and makes a contract with her.

Upon returning to the real world, he finds out that 10 years have passed. In order to find out what his sin meant, he began to work under Break as part of Pandora. During this, it is shown that when he was young, he worked hard to gain praise and recognition from his father. However, he had discovered that his father hated him to the point of not wanting to touch him. After experiencing this, Oz began to think that there is no guaranteed thing in the world. He thought of himself as weak and, in order to protect people, he should at least remain an obedient child and let harm come his way.
After traveling into the Cheshire Cat's realm, Oz meets Jack Vessalius and in turn becomes his "medium." Jack eventually speaks at Pandora's headquarters and the public hail Oz as a "hero." Oz finds that he can swap consciences with Jack if he calls hard enough and may sometimes even see snippets of Jack's memories. According to himself he is quite skilled with the sword, particularly in self defense. However, he has no real experience in fighting. Oz likes cute, younger girls and flirts with them frequently. He once wished to marry Sharon when they first met. In chapter 20, Oz called Alice "my most precious Alice," but it is not known if these feelings are sincerely his or Jack's since he resides in his body.

Oz's body is not actually his but the de-aged body of Jack Vessalius. His original form is actually that of two stuffed rabbits, given life unintentionally by Lacie. Many years ago, one of these dolls resided in the Abyss with the Intention of the Abyss and the other with Alice outside. After Jack lied to the Intention of the Abyss, saying he wanted to come and see her, she asked Oz to guide Jack to her. Oz agreed and traveled through one of the Doors of the Abyss. After Jack asked him to form an illegal contract, Oz warily accepted. However, upon the formation of the contract, Jack ordered him to sever the Chains of the World. Forced into submission, Oz had to comply, and this ultimately caused the Tragedy of Sablier. As everyone was dragged into the Abyss, Jack was not due to seeming foreign to the Abyss. His body froze at his age and started to regress, slowly destroying Jack's mind but not Oz's which remained dormant in him. Many years passed, and as Jack neared regressing to infancy, he approached Zai Vessalius, telling him to take him in as his son. Unaware of Jack's true nature until later, Zai accepted. Then, Jack's mind in shambles and body an infant's, Oz had full control of the body though no memories of the past.