Black days ahead. That was sure the case with the Aquamen. On Earth-One, a technologically savvy pirate going by the alias of Black Manta of the underseas scoured the depths seeking to plunder the resources of Atlantis and set up an empire of his own minions. On Earth-Two, it was a more low tech but creatively diverse Black Jack who along with his sadistic minion pirate band caused repeated torment for the golden age king of the seas.
Not much was known of either criminal, certainly not there alter ego nor their true origins, only rumors. Black Jack oscillated from one-eyed to dual optical clad cad. Black Manta was portrayed fairly more consistent, with his stylish helmet generating tremendous bolts of energy through the optical lenses. While Manta had 17 appearances on Earth-One, his counterpart had only 12 chronicled. However, both were "old foes" of the Aquamen before their first appearance so chances are there were far more meetings of the two.
They were also notable for having other foes, in the form of yesterdays Ocean Master and Sea Sleuth, both of whom having ties to their respective Arthur Curry's as brother or friend. Manta exceeded the terror wrought by Jack, however, when he took the life of his arch-enemies' young son Arthur Jr (Aquababy). Each were fit for the keelhaul. Arrrr.