Sea Horror

Golden Age Origin
The Sea Horror originally claimed to be an undead sailor who guarded millions of dollars worth of gold in the hold of a sunken ship. He appeared to be capable of "living" underwater without oxygen, and also seemed to have some degree of control over sea animals.

Later it was revealed that he was actually a nazi agent wearing a mask that supplied him oxygen from a small tank concealed under the hump on his back. Apparently he was trying to retrieve the gold to fun the Nazi war machine. However, his ability to breathe and talk without a visible mask seems unlikely, and does not explain his ability to command a giant octopus.

Golden Age Appearances
Dynamic Comics #9