He is Dave, Fang and Candy's uncle, on Glimia's side of the family, though this is based solely on appearance. A rather clumsy sorcerer who usually wreaks havoc with his spells rather than being useful. It was revealed in the episode "Sorcerer Material" that he never really went to sorcerer school, he just worked in the cafeteria.
Uncle Oswidge loves to eat and presents a rather unkempt appearance. Like his younger niece Fang, he secretly likes to play with dolls. His favorite foods are ham and "Nut Logs" - he cannot resist them. His knowledge of magic and magical items, and most other things, surpasses the rest of the family.
His name is a pun on Oz, as in "Wizard of Oz", considering he's a wizard.