- Human Flying Fish was originally Victor Bragg, who thanks to the surgery of his associate Doctor Krill, gained the ability to literally fly as well as swim fast and survive for extended duration under the sea. He battled Earth-One's Aquaman.
- Seaman was an alien from another world who crash landed on Earth-Two, and recruited that world's Aquaman to help him repair his craft after several acts of saving others.
- Poseidon was an android created by the mother of Earth-One's Aquaman, with the memories of his father Tom Curry, and granted aquatic powers and the ability to control fish.
- Mister Neptune was a conman who used a rocket powered trident and other gadgets to give him "godly" abilities versus Earth-Two's Aquaman.
- Cutlass Charlie and Captain Flint were two wannabee pirates employing old fashioned gear versus the Aquamen.
- Marine Marauder and the Master of Marineland employed technology to mentally control fish versus the Aquamen.
- Several other individuals bedeviled the Aquamen of two worlds over the years. From men in deep sea diving suits to pseudo-aquatic creatures to legitimate threats.
Among the greatest threats versus the Aquamen were Black Manta and Black Jack, each mirroring their counterpart in acts of piracy and repetition of attached versus the arch-nemesis. The only rival to them beside their blonde hair foes were the water wonders that were Ocean Master and Sea Sleuth.
While neither Earth-One's Black Manta nor Earth-Two's Black Jack ever revealed their true identities, their motives were obvious. And the technology they used was unmatched even among their various peers.