Whatever Happened to the Golden Age Aquaman

The scenario: A device from across the universe arrives in orbit over Earth-One. From this object, rays are projected that manipulates dimensional time reflex, which causes the "black city" of Necrus to appear. The soldiers from Necrus attack a nearby undersea settlement of surface dwellers and obliterate it, given its ruler's xenophobic nature. When Aquaman hears this, he recalls past encounters with this ruler, Mongo.

Although the villain traps him in an impenetrable bubble, another beam from the alien object causes a second Aquaman to appear and lead the Atlantean armies against Necrus. He defeats  those forces, though at the cost of his life. After a funeral, the native Aquaman appears and along with his wife Mera defeats Mongo, who retreats to his city that vanishes from whence it came.

When examined further, the identity of the second Aquaman appears to clarify with the clues presented in this tale. First, the alien orbiter opens dimensions and time to transferring objects from one location to another. Second, the Earth-One Aquaman recognizes the city of Necrus, though it is not native to his world's oceans  Third, when the second Aquaman appeared, it was assumed that this was a clone although the same ray didn't clone Necrus but simply materialized it and its citizens into Earth-One's dimension. This indicates that the other Aquaman was from another dimension and possibly an earlier time. Finally, the imprisoned Aquaman used his own telepathic connection with the other version of him to mentally guide him, until that one died. Aquaman's Justice League allies held a funeral for his twin.

It appears that this other Aquaman originated on Earth-Two, the only other Aquaman known to exist in the pre-Crisis Multiverse. It was he who had previous battles with Mongo and his minions when their city appeared periodically. This Aquaman last appeared in the fall of 1956, and so given the twenty year vibratory gap between the two universes, would appear on Earth-One at a time when he was biologically the same age as his counterpart.

There is precedent for counterparts sharing memories and merging with one another. When the Supermen of Earths One and Two merged in order to battle Krogg, they acted as one. And later, when Atoman of Earth-Two journeyed to Earth-One, that world's Superman suddenly gained memories of his counterpart due to the dimensional transfer.

It was the golden age Marine Marvel that passed away and was honored by the Justice League, unaware that this was the Aquaman from the universe of their friends in the Justice Society. Mongo and Necrus returned to their trans-dimensional existence after defeat.

And so answers the question as to whatever happened to the Golden Age Aquaman.