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 Shalon 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.
Jack tells Oz that has the "right" or "perquisite" over Alice's power and that a seal won't restrain Alice's powers any longer, making Oz have the ability to use B-Rabbit's power even without Alice's permission or Gil's help. Oz proves it when he was able to stop Alice's B-Rabbit's power temporarily on his own; another time when Oz was almost kidnapped by the Baskervilles at Latowidge, and then recently when he was able to summon B-Rabbit's scythe to fluently fight his assailants inside Sabliers illusion, despite the fact he had never used a scythe before. (He doesn't seem to notice this though). According to Lotti, Oz was suppose to be the vessel for the sake of hiding the existence of Jack Vessalius and should the vessel be broken, Jack’s existence will be brought to light and the further warping of abyss’s will, who seeks for him, will most probably interfere with the real world. Later, Oz reunites with Gilbert and immediately meets with the person behind Oz's suicidal nature: Zai Vessalius, his father.
