Well, that's a tough one. It could be argued that characters like Superman or Thor are among the most powerful, but it really varies depending on the specific fictional context and the rules of that world.
The determination of the most powerful fictional character is subjective. Some might consider characters like Goku from Dragon Ball or Doctor Strange as extremely powerful, but it all comes down to how their abilities are portrayed and the challenges they face in their respective stories.
It's hard to say for sure. Different fictional universes have their own powerful characters and it depends on various factors like their powers, skills, and storylines.