A square jawline. A protuberant chin. A manly cleft. Somewhere along the line (possibly around Superman's time), artists decided that these, more so than anything else, were the defining facial feature of really heroic (or really strong and dumb) characters. Perhaps to an even greater extent than broad shoulders, barreled chest, and absurdly large biceps, the surest sign of a character's strength and manliness lies in his chin. This has some Truth in Television, as scientists have noted that there is a definite correlation between jaw size and testosterone production.