It depends, would he/she turn into an normal boring human being? Or would they stay the way they are in whichever fiction they come from, with all powers and abilities?
At the top of my head, I guess it'd be something like that spider that bit Peter Parker.. I'd have it bite me, and then I'd be awesomest. There's probably something better, but it's late and I'm somewhat sleep-deprived..
only 1 character? Just them being alive? hum... I'd say, Piccollo. He wanted to rule the world, he can have ours, he'd be most likely better than any of our current politicians.