Let's face it. Nobody can fight super-villains for over fifty-five years without hitting a few clunkers. All heroes of long standing have battled villains who were, shall we say, less than threatening. Superman has had Terra-Man, the Master Jailer, and Blackrock, among others. Batman has faced Killer Moth, Cavalier, and the Ten-Eyed Man. Wonder Woman's foes have included Angle Man, the Blue Snow Man, and the immortal Egg Fu.
Aquaman is no exception. Indeed, moreso than most, the Sea King's rogues gallery seems clogged with lame bad guys. Villains so inept, you wonder why Aquaman didn't dispose of them in two panels.
For your edification, and probably amusement, here's a look at a few of the lamest. At no time did I make any of this up. Honest.
Quite possibly, the lamest Aquavillain of them all. This gaudy yellow-and-purple costumed crook could move equally well under the water or through the air. He appeared just once, in the canonical DC Universe; ADVENTURE COMICS #272. (He also appeared in the first two issues of SUPER FRIENDS.)
A "human electric eel", this man was immune to electricity. He wore a lightning rod on his head to attract lightning bolts and "charge" his body with deadly current, so no one could touch him while he committed crimes. He fought Aquaman in ADVENTURE COMICS #254; he was also a member of the first team of super-villains to face the Justice League, in JUSTICE LEAGUE OF AMERICA #5, fighting alongside such master villains as the Getaway Mastermind and Professor Menace.
In ADVENTURE COMICS #441, Aquaman returned to that title after a 14-year absence. His return was somewhat ignominous, as he defended Atlantis from the invasion attempt of a hook-handed villain dressed in Gilbert & Sullivan pirate garb with a scuba mask and tank.
An unethical scuba diver who tricked Aquaman and Aqualad into recovering for him a sunken chest, containing a magic potion that transformed him into a twenty-foot-tall purple-skinned monster. The Creature King debuted and departed in SHOWCASE #32.
An interesting case here. In many Justice League stories of the 60s, like the aforementioned JLoA #5, the JLA fought teams of villains comprised of one enemy of each regular member of the team. Aquaman's rogues gallery was so poor in those pre-Ocean Master & Black Manta days, that on three separate occasions, the writer created brand-new villains for the stories and called them "old enemies" of Aquaman. None of them have ever been seen again.