Test pilot Chuck Chandler was caught in the explosion of an alien spacecraft and ended up as a 2-D image on the glasses his brother Hal was wearing. By wearing the glasses and concentrating, Hal could bring Chuck back into 3-dimensional space at the 3-D Man, with three times the speed, strength and agility of a normal man!
Notice how cleverly it all ties into 3-D movies - the glasses, the red & green costume, the "three times a normal man" powers. It's genius. Sheer, misguided, weak-idea-stretched-dangerously-thin genius.