The Ocean Master is, far and away, Aquamn's greatest foe. Their battles have raged above the waves and below, drawn many other heroes and villains into their conflicts, and even though Aquaman has always won, in his heart he has lost, for his most relentless enemy is also his own brother.
The Ocean Master first appeared in AQUAMAN(1st series)#29. He was a costumed high-tech pirate then, attacking ships on the open sea. Aquaman set out to bring him to justice, but Aqualad could tell there was something about their foe that Aquaman was not revealing. At the end of the story, Aquaman confided in his young partner that Ocean Master was his own half-brother, suffering from amnesia. But this brother, Orm Curry, had always resented his older brother, clearly their father's favorite; even before the accident that gave him his amnesia, he had sought to escape from his brother's shadow through acts of rebellion and crime.
Ocean Master fought Aquaman several times more while still in his amnesiac state--once battling Black Manta for the right to kill their foe (AQUAMAN #35). When the master criminal regained his memory, and learned that Aquaman was his brother, he tried to halt a plan he had put into motion to destroy Aquaman (AQUAMAN #50); but apparantly he soon remembered his resentment of his elder brother, for he was quickly back to his attacks on the Sea King.
The brothers' struggles have never been very private ones. Several of Aquaman's colleagues in crimebusting have been drawn into their conflicts, such as Superman (DC COMICS PRESENTS #6), Batman (THE BRAVE AND THE BOLD #82), and the Teen Titans (TEEN TITANS[1st series] #28-30). Ocean Master has not been above allying himself with other villains to achieve his ultimate goal of Aquaman's death, either. He worked with the Shark in the latter's attempts to take over Atlantis (ADVENTURE COMICS #444), and he was one of several super-villains gathered by the Queen Bee to destroy the Justice League (ACTION COMICS #443).
Ocean Master has, on certain occassions, used powerful, highly-advanced robots, which he himself apparantly designed and built; one called Seaquake (AQUAMAN #62), and a robot double of Black Manta (ADVENTURE COMICS #478). These robots were so well-designed, Aquaman could not tell them from the real thing.
In the 1986 AQUAMAN limited series, Ocean Master's final pre-Crisis appearance, he eschewed science in favor of sorcery. He discovered the hiding places of six mystic crystals, remnants of the pre-cataclysmic Atlantean civilization, and used them to attack his brother. Aquaman, with the aid of an undersea sorceress named Nuada, was able to overcome Ocean Master on the mystic plane, using his own love for his brother as a weapon. The magical backlash apparantly destroyed the Ocean Master.
The post-Crisis restructuring of Aquaman's history leaves Ocean Master's role in it confused. It is uncertain which of his pre-Crisis appearances, if indeed any, are still canonical. In the fourth and final issue of the AQUAMAN: TIME AND TIDE miniseries, Ocean Master's first meeting with Aquaman is recounted. Here, he shows up at Atlantis and demands that Aquaman fight him for kingship. Neither man is aware of their relation, and Aquaman only learned of it much later by reading the Atlantis Chronicles. When Ocean Master next turns up, in AQUAMAN (current series) #19, he is leading a small civilization of offshoots from Atlantis, and wielding mystic powers given him by Neron, the demon who empoered DC villains in the UNDERWORLD: UNLEASHED saga. He is about to kill Aquaman and Dolphin, when Aquaman tells him of their relation; the resulting confusion disrupts his concentration and destroys his power.
A somewhat different version of Ocean Master, as well as Aquaman, was seen in the 1996 AQUAMAN ANNUAL. All DC Annuals that uear were written on the theme of "Legends of the Dead Earth"; thousands of years in the future, Earth has been abandoned by its people, and its heroes survive as legends. One such folk-tale told of an Aquaman who ruled the seas with an iron hand, exacting tribute from those who sailed them; the heroes who failed to stop hi; and Ocean Master, along with Black Manta, who offered to do so in exchange for untold wealth and immortality.
It is certain that the Ocean Master will return some day to plague Aquaman anew. He is yang to Aquaman's yin; so long as there is an Aquaman, there will be an Ocean Master to oppose him.