Daniel Ozborne (Oz) is the definition of cool. As a senior and the guitarist of the Bronze-playing-band Dingoes Ate My Baby, he holds the standard.
He first appears in season 2 on career day and was the only one in the school apart from Willow to be picked out to represent Sunnydale High, and they are given the chance to work for a computer company. Neither of them takes up the challenge, and when Willow asks him what his plans for the future are, he answers mastering a chord on the guitar.
However, he discovers the fact that when his cousin Jordy bit him, he turned him into a werewolf. Not wanting to harm anyone, he locks himself in the library cage on the nights before, after, and during the full moon. The Buffy gang discovers this too when Willow comes round to his house to ask him why he hasn't kissed her yet. Oz turns wolfy, and chases her across town, but Buffy manages to sedate him with a tranquilliser gun.
Oz shyly flirts with Willow, first seeing her at Halloween in her rather revealing ghost costume. When he plucks up the courage to ask her out, they start dating and soon the two are as happy a couple for a year.
But Willow, at the moment she thought she was going to die, passionately kisses Xander while Oz and Cordelia look on in shock. Oz is prepared to give it a try because being without Willow is like being without '-an arm. No, worse, a torso.'
In the episode 'Beauty and the Beasts' he faces the guilt that he might have broken out of his cage and brutally killed someone. The fact that the murder was in the daylight, however, clears his name, but it worries Oz for a while.
Everything is normal in the life of Oz, or what goes for normal in Sunnydale, the scoobies fight the mayor, and Oz and Willow consummate their relationship on Graduation Day, which is Oz's version of panicking.
When Willow starts college Oz already knows the people there, and feels comfortable wherever he is. The Buffy gang is invited to a frat party, and Oz brings his bass set to wire it up. Unfortunately he cuts himself, and drips blood onto a symbol painted on the floor. The symbol brings forth the fear demon and to his horror, Oz feels himself beginning to change. Fortunately he manages to stop himself, and Buffy vanquishes the demon.
In season 4 he starts to notice Veruca, the lead singer for the band Shy. Oz finds out the fact that the attraction stems from the fact that she is also a werewolf, when he breaks from his cage and mates with Veruca. He knows that Buffy will kill Veruca if she is let outside on the full moon, so he invites her into his cage. They mate again, and when Willow comes to bring Oz food the next morning, she is distraught. She rushes to the science lab and prepares to curse Oz and Veruca, but she can't do it. Veruca finds her and prepares to kill Willow, but Oz kills Veruca in wolf form. Oz decides to leave Willow and Sunnydale because of what something Veruca says- 'The wolf is inside you all the time, and your human face is just a disguise'. He drives off in his van.
Willow has a hard time getting over him, but she finds a deep and lasting bond with witch Tara, and when Oz comes back to her with his full moon frolics under control, she chooses Tara. Oz leaves again. Maybe forever.