Aquaman #9

From the depths of 1963 comes this vivid Nick Cardy cover pitting Aquaman and Aqualad against a truly mythic threat. A regal, white-bearded figure astride a massive green sea serpent looms menacingly over the two heroes, trident in hand, declaring their doom — while Aquaman himself gasps that Neptune "was only a legend." The story title "The Secret Mission of King Neptune" promises exactly the kind of larger-than-life underwater adventure that made this Silver Age series such a treat.