Fantastic Four (1961) #20
First appearance and origin of the Molecule Man. "The Mysterious Molecule Man!" is written by Stan Lee and drawn by Jack Kirby and Dick Ayers. The FF are in the midst of a normal Saturday afternoon (you know, Reed is studying a bizarre meteor rock while Sue tries to keep Ben and Johnny from killing each other), when their routine is interrupted by the presence of strange, glowing blue ball in the middle of the street. Upon investigation, the group finds the ball is a dimensional doorway to the home of Uatu, the Watcher.
The Watcher warns the FF of an amazing new threat that could imperil the entire universe. A no-name laboratory technician beneath even his employer's notice has been imbued with atomic power. His newfound abilities include an incredible talent for re-arranging the molecular structure of inorganic material. With a wave of his wand, the self-dubbed Molecule Man can create any object or force he can imagine and he uses that power to assume control over New York City. It's up to the Fantastic Four to somehow stop the Molecule Man and they'll call upon the talents of blind sculptor Alicia Masters to do it!