Man-monsters are popular in fiction for their tragic nature and fascination with blending human intellect with superhuman physique. And then there are the monsters of the heart. Prime examples of these twin concepts are the following:
Juan Vallambrosa was the victim of the machinations of Captain X aka Jonathan Dorrance, an amoral sailor, transformed into a powerful gigantic beast named Man-Fish of Earth-One. Seeking revenge against Captain X whom he transformed for his new inhuman form, Man-Fish was drawn into various confrontations with the Sea Devils led by X's son Dane, often as he sought methods to transform himself back to human that would've caused devastation on humanity. Each time, he began the tale as a foe and ended as an ambiguous ally retaining a semblance of a human heart. His doppleganger, Juan Vallambrosa of Earth-Two was the genetic mutant known as Carcharo. Experimented on by a geneticist named Doctor Love, this Juan along with his cousin Yolanda and half a dozen other babies grew into freaks as adults. In his case, Vallambrose became literally a shark-man. At first enlisting the aid of his fellow mutants in Helix versus the heroic team of Infinity, Inc., Carcharo soon perished after being bitten by the cyanide teeth of Helix's leader, Mister Bones.
On Carcharo's world, decades earlier, was another prey of the deep in Black Shark. This villain was the arch-enemy of the Red Torpedo, facing the hero and his fiancee Meg on eleven occasions. He often allied with Torpedo to fight common foes such as the Dweller of Caverns, although his true agenda was always self-centered. What became of this fiend after his adversary joined the Freedom Fighters and left for Earth-X, never to return, has been undocumented. And it was his counterpart, Killer Shark of Earth-One, who was the perpetual arch-nemesis of the Blackhawks of that world. So much of a threat was he, that he actually brainwashed that team's agent Zinda Black and transformed her for a time from Lady Blackhawk to Lady Killer Shark. What became of him after his numerous defeats has been undocumented.