Daniel 'Oz' Osborne
Daniel Osbourne, referred to exclusively as Oz, is a fictional character in the television series Buffy the Vampire Slayer, played by Seth Green.Warning: Plot details follow.
Oz was introduced as a romantic interest for the character of Willow Rosenberg. His most notable characteristic was his detached and taciturn approach towards things, which masked a deeply philosophical interior. He was also the lead guitarist for the band Dingoes Ate My Baby, which regularly played at The Bronze.
In the episode Phases, it was revealed that Oz had become a werewolf, turning into the wolf the three nights around a full moon, due to a bite on his hand from his cousin Jordy. His lycanthropy led ultimately to his character leaving the show in Wild At Heart, where he killed another werewolf Veruca, and felt that he would cause harm to Willow and others.
He returned later that year in the episode New Moon Rising, believing that he had found a cure in Tibet. However, although the moon no longer affected him, he could still transform into the werewolf when faced with strong emotion, such as anger, fear, or pain, as he discovered when realizing that Tara Maclay had replaced him in Willow's affections, and when The Initiative took him for their experiments.
After that realization, Oz left Sunnydale for good, returning only during Willow's dream sequence in "Restless".
Further information: Monosyllabic Tendencies