As a result of the cosmic ray exposure during the space flight he took with his sister, Susan, Reed Richards and Ben Grimm, he gained the most spectacular set of powers. Namely, he can harmlessly envelope himself in flame at will which allows him to fly, shoot flame offensively and absorb heat energy.
As the youngest member, he has proved the most impestous and was given to many of concerns of teenagers. This includes a playfully antgonistic relationship with Ben Grimm. This hit a low point when Johnny fell in love with Ben's old flame, Alicia Masters and married her, only to learn that she was a Skrull[?] imposter named Lyja[?].
wikipedia.org dumped 2003-03-17 with terodump