It was on his initiative that the fateful space mission which had Susan Storm, Johnny Storm and Ben Grimm accompanying him into space took place. In space, they were exposed to cosmic radiation; when they crashlanded and found that their bodies were changed dramatically, it was Mister Fantastic's suggestion that they decided to use their new abilities to serve mankind as the Fantastic Four.
To that end, he created numerous exotic devices and vehicles for the team to use such as clothing made of unstable molecules so it can be used with their powers safely. Furthermore, he often leads the team into daring expeditions such as into the Negative Zone in addition to opposing evil. In addition, he has felt personally responsible for Ben Grimm's grotesque change and has laboured off and on to reverse it permanently.
Unfortunately, there are drawbacks to his association with the team. Chief among them is that the team's violent encounters with Doctor Doom are on account of his irrational grudge against Reed for supposedly sabotaging his college experiment that scarred him.