Aquaman Allies and Adversaries: The Sharks

This time we spotlight two characters who were opposite sides of the exact same coin. There was the mutated Shark, originally a shark that upon gaining irradiated intelligence was a foe of Earth-One's Green Lantern. Mutated by atomic radiation into becoming a  humanoid, he gained telepathic and telekinetic powers. The Shark created the disguise of a business-suit clad man, seeking prey that would challenge him as per his natural instinct. The Lantern, being a man without fear, became the perfect foil for this future felon. After a couple encounters with the Emerald Crusader as well as one case involving the Justice League, the mental madman turned his attention to Superman and found a similar result as he was once more returned to his original form.

After these string of defeats, the finny foe turned his attention to fellow dweller of the deep, Aquaman. Attempting to claim the Earth-One Atlantis by adopting a human form as Karshon, a usurper to the Altantean throne, he enlisted foes such as Black Manta and Fisherman in his schemes to distract their mutual foe. In the end, they all met defeat and had to bow to the true master of the seas! When the Shark returned some time later for a rematch with his arch-enemy, he was more bestial in nature than before and nearly vanquished Green Lantern, before the hero found the will power to overpower Shark's fear factor.

Decades previous on Earth-Two, a felon known as King Shark encountered that world's Green Lantern, only his goal was to redeem his name prior to his execution for the crime of murder. However his mysterious appearance and seeming superhuman powers made him a force to be reckoned with by friend and foe alike.

A few years later on Earth-Two, Shark Wilson attempted escaping the clutches of the law, diving into legendary waters that were said to transform men into beasts. Sure enough, when Aquaman tried to track down his prey, he ended up himself an endangered species! In the end, the shark disappears and Wilson returns. While the Shark had the same motivations as Wilson, not to mention the same first name, there was no definitive evidence to either confirm or deny whether the rather human looking face on the fatal finned fish was tied to the crook. Nevertheless, this was a memorable exploit that has been reviewed periodically. Wilson's Earth-One counterpart was Shark Norton, who faced his world's Aquaman as well although unlike Wilson didn't transform into a human shark.