The X-Men #52

From January 1969, this Marvel issue carries the ominous title "Twilight of the Mutants!" and delivers a cover — penciled by Marie Severin and inked by Joe Sinnott — that radiates genuine menace. A towering red-armored villain with horned helmet dominates the foreground, while the blue-rendered X-Men — including a winged figure soaring above and several teammates hurled or scattered across a debris-strewn battlefield — reel from a blinding burst of energy. It's a beautifully composed image of mutants under siege that perfectly captures the high-stakes tension writer Arnold Drake and artists Don Heck and Werner Roth brought to this era of the title.