Croc Head is one of the least popular Fatman enemies there are. He is sometimes considered as the ugliest one, but he does have some competition, and some more.
He was born in Possum City, but he had a disease that turned him green and ugly. His parents abandoned him because they are Humans, so that is their natural reaction to people as pretty as Croc Head.
He grew up as a monster in the Possum City sewers. This is where the Sewer Gator legend came from.
Eventually, Creepy Mask Man discovered him, and boosted his powers, making him even uglier. He hated this, but still did what he was told. After he was beat by Fatman, he abandoned Creepy Mask Man and went on to live a better life. This was told in the film Fatman 5: Get a Life.