Source: dc.wikia.com

3. The Shark

Aside from looking like the mascot for a brand of Nineties fruit snacks, The Shark also made a name for himself fighting Aquaman and the Green Lantern.

A shark was minding its own business one day, swimming around the ocean and getting up to shark shenanigans (Shark-nanigans?), until it was irradiated and mutated into a shark-man. He then took up the bold and innovative name of…The Shark (YES, WE HAVE TWO SHARK GUYS ON THIS LIST, THERE IS NOT MUCH VARIETY HERE). He also took a human name, despite being very clearly a shark-man. That name? T.S. Smith. The T.S. stands for Tiger Shark. Tiger Shark Smith. Is it any wonder this guy lost to Aquaman?

He's much more frequently called Karshon, which is a minorly better name. He is a shark-guy. This is the extent of the information I can provide. He also fought Aqualad once.

Why he isn't more popular: Despite being the better shark guy, that dubious honor still can't make him cool. Sadly.