Although he began as just a man with crocodile-like skin, over the years, Killer Croc's appearance has grown more and more inhuman. He now has a more bestial form, complete with a truly reptilian head, razor sharp claws and teeth, and he even has a tail.

Why did Killer Croc grow a tail?

Killer Croc is apprehended in his hideout, the Gotham City lighthouse, and incarcerated by Warden Ranken and the Iron Heights Guards. ... In this pretext they also experimented on Iron Heights Prisoners. This trauma caused Croc's condition to get even worse, growing a tail and now really resembling a giant crocodile.

How did Killer Croc become a crocodile?

Killer Croc, born Waylon Jones, is a criminal and nemesis of Batman. He was born with an extreme form of the medical condition Epidermolytic hyperkeratosis, which caused his appearance to develop progressively into that of a crocodile, hence his name. His mother died in childbirth, and his father abandoned him.