The villain King Shark has become a more popular character in recent years, in part to his (wildly different) appearances in the animated Harley Quinn series, the newly released The Suicide Squad, and the upcoming videogame Suicide Squad: Kill the Justice League.
Before that, he was a relatively minor fan-favorite in the DC Universe, with his recent appearances focusing on the Suicide Squad and his conflict with Aquaman. But when he was introduced in the Post-Crisis DC Universe, King Shark had a more consistent (and somewhat surprising) nemesis -- Superboy.
Despite often being pitted against the likes of Aquaman -- which makes sense, considering their matching natural envoronments -- King Shark debuted in Superboy #9 by Karl Kesel and Humberto Ramos. After briefly appearing in a brief cameo in Superboy #0, Nanaue is introduced as the man/shark hybrid son of a powerful "King of All Sharks" -- essentially a god for the predatory species. Living with his mother in Hawaii, King Shark ran afoul of Superboy when the young hero and his friend Tana came to the beach. Despite his relative lack of power compared to Superboy, King Shark actually gave the young clone a tough fight in the underwater caves of the island.
King Shark and Superboy would soon work together as part of the Suicide Squad to bring down the criminal organization known as the Silicon Dragons. Superboy's tensions about King Shark remained at the forefront, with the young hero expressing concern about how vicious he could be. King Shark would survive the mission (albeit under the assumption that he was killed in an explosion), and eventually, face off with the Boy of Steel again multiple times. King Shark slowly transitioned away from Superboy, however, with the "One Year Later" event positioning him as a foe of Aquaman and Atlantis. But the feud between King Shark and Superboy was recognized in another fan-favorite series.
When King Shark later joined the Secret Six, he got the chance for a rematch with Superboy. In the final battle of Secret Six #36 by Gail Simone and J. Calafiore, with the small team of villains cornered by a small army of heroes, the entire group decided to take Venom and go down fighting. During the ensuing chaos, King Shark can be seen throwing down with Superboy and even seemingly injuring him -- only to be brought down by Supergirl. Despite making sense as an enemy for Aquaman, there's something to be said about King Shark being a foundational Superboy villain.
King Shark was someone the typically aloof teenager couldn't just brush off. Seeing one of King Shark's victims in Superboy #9 even left the Kryptonian clone vomiting and shaken, and their fight underwater was one of the Boy of Steel's earliest true brushes with death. King Shark is an interesting figure to imagine as a consistent Superboy enemy, especially in the Post-Crisis DC Universe.