Aquaman, the King of the Seven Seas, is also known by his human name of Arthur Curry. This secret identity for the character has been part of his history since the Silver Age and remained even after the Post-Crisis DC reboot changed his origin. Though he remained the son of Atlantean queen Atlanna, many other elements of his character were dramatically changed. Not only was he no longer half-human, but eventually, he was replaced by a completely different character.
Arthur Joseph Curry had the same name as the true Aquaman, as well as an uncanny resemblance to him. Despite these similarities, he was seemingly unrelated to the classic hero, who had mysteriously gone missing. Entangled in a Lovecraftian fantasy that dealt with the fallout of Atlantis' destruction, the second Aquaman eventually disappeared, never be heard from again.
The Sword of Atlantis
Arthur Joseph Curry's adventure began in Aquaman: Sword of Atlantis #40 by Kurt Busiek, Jackson Guice and Daniel Brown. Despite the title, this "new" book continued the numbering of the previous Aquaman volume and played out in the shadow of Atlantis' destruction and the fate of Sub Diego. The original Aquaman had communed with the various Sea gods in order to restore Sub Diego, and in doing so surrendering his mind, body and soul to their whims. This left him as a derelict, inhuman monster named the Dweller in the Depths, whose terrifying visage combined the appearances of several sea creatures.
His mental abilities now greatly expanded, the Dweller psychically reaches out to the man named Arthur Joseph Curry. The Dweller believes that he is the true Aquaman and misremembers his own life as Aquaman as a cryptic prophecy. He befriends Mera after freeing some of the surviving Atlanteans from slavers, allies himself with former villain King Shark and befriends Topo, a humanoid cephalopod who homages Aquaman's Silver Age pet octopus. Unfortunately, this growing circle of friends would soon begin to dwindle, as Arthur Joseph Curry's tragic nature was finally revealed.
Dweller in the Depths
The Dweller seemingly died in an attack foretold by an amnesiac Garth. To make things worse, the new "Aquaman's" history was finally revealed to him by the Lady of the Lake. Arthur Joseph Curry was in fact a human and had the uncanny ability to breathe and physically survive underwater thanks to an experiment conducted on him as a child by his father. This referenced the forgotten Golden Age Aquaman, who wasn't Atlantean but merely a mutated human. This experiment was later used by Anton Geist to mutate the citizens of Sub Diego. Unfortunately, his initial inability to breathe on land saw him apparently die when his aquatic tank was destroyed in a storm.
The boy was named Arthur after the original Aquaman, who had given the boy's father a sample of his mystical water hand in an attempt to save his life. When Aquaman sacrificed himself to raise Sub Diego, part of his soul attached to Arthur Joseph Curry via the water hand sample, restoring the young man to life while mutating the original Aquaman's body into the Dweller. The new Aquaman blames himself for both of the original's deaths and now swore to only answer to his middle name.
The new Aquaman didn't acclimate himself much to the wider world of superheroes. After being rejected by Batman's Outsiders due to inexperience, he and King Shark both opposed Batman and Superman's desire to remove all traces of Kryptonite from Earth, including Atlantis. His status as Atlantis' new king didn't earn him much popularity, either, as the people simply saw him as a reincarnation of Orin, their name for the original Arthur Curry. When Garth tried to meet with him in Atlantis, he discovered that Arthur Joseph had left the Aquaman costume and trident behind, relinquishing the throne and the Aquaman title.
The true Arthur Curry would finally be revived once and for all through the events of Blackest Night, reuniting with his wife Mera and returning to Atlantis. It's unknown what effect this had on Arthur Joseph Curry and his soul, with the second Aquaman having never been seen again. With the subsequent reboot of the New 52, it's likely that the fate of this would-be King of the Seven Seas will forever dwell in the depths.