The Shark (Karshon), an old GL villain who seems more suited to Aquaman, having a rewritten origin story.. an improvement upon the character.
Less "sharks are scary and evil" and more like.. focusing further on the whole pollution thing that is stated in his origin and debut comic.
Also.. why not play around with the species of shark he is?
if I had my way I'd go with my favorite shark, Goblin Shark.
I like to think of this new version of Karshon started off being encountered by and fighting off against the Green Lantern, but after some time of retreating back into the sea, he comes across Atlantis. He takes a form somewhere between human and shark to try his best to blend in with the aquatic humanoids, learning about them to see if they're a friend or foe to him. This leads into him becoming an enemy of Aquaman and ultimately becoming one of Aquaman's recurring villains within his rogues gallery.
Karshon is his real name from when he was a shark. That's the only thing he has from that time aside from his knowledge and memories. other sharks have names, too. After all, sharks can recognize familiar members of their kind.
He may not be a super genius intellect type, but he is capable of solving problems and puzzles quite well. He's quite adaptive and fast at learning, this adds to the level of a threat he poses. Although, he mostly just wants to be left alone.
As a Goblin Shark, he isn't necessarily the fastest at moving.. but his bite? Watch out for that! It can be nasty.
I think.. as a villain.. he's both curious and wanting to learn about this terrifying new world, indulge in the new expanse of potential food for him to eat without having to worry about not getting enough like he did back in the deep. He does have a strong distaste for pollution and the harm that the humans do to the ocean. After all, it's those radioactive polluted chemicals that found their way down to the depths where he swam and changed him.
He does not think himself as a higher being of evolution nor does he possess psychic powers like Gorilla Grodd, and he isn't like King Shark by being the powerful descendant of a god. He was just a normal shark swimming peacefully and leisurely in the sea when those chemicals rained down and engulfed him. Some may say he got the short end of the stick, but he's not a creature to be underestimated. He still puts up a good fight and knows enough of what he's doing.
Altered abilities:
Can change his appearance from human to shark and somewhere in-between at will. He figures this out sometime after his inception/evolution on max speed. This ability allows him to blend in both on land and in the sea. it also makes him a bit of a threat this way to those he deems a threat to himself and what he deems his territory.
Human level intellect. nothing really special here, but he does learn human speech (english) and even atlantean. it is when he is able to speak and communicate with other people that he reveals his name. He remembers his life as a shark and all he knew. he still has those instincts, but he lacks a full understanding on the human world. the world above the waves. (despite learning the language, he is a man of few words and likes his solitude)
Impressive strength and a terrifying bite, even in his humanoid forms. Regardless of the evolution, his body still retains some elements of his original shark form; rows of sharp teeth, electroreception, and heightened senses. Can likely also jut out his jaw like the Goblin Shark he original is. his heightened senses and electroreception makes him quite the foe when provoked. As well, due to his life originally as a shark, he is highly skilled at swimming and traversing any water.
