Many authors picture the Obstacle Character as a negative or evil twin. Although this can be true, it has little to do with the Obstacle Character’s dramatic function. For example, if a Main Character is evil and needs to change, their Obstacle might be a virtuous steadfast character. Or both characters might be evil, with the resolve of one contrasting the change in the other. In any case, the function of the Main and Obstacle Characters is to show two opposing sides of the same issue. That is their story function: to show what happens when one changes and the other remains steadfast on a particular issue.
From the Dramatica Theory Book