The Werewolf of Fever Swamp
The swamp hermit was believed to be the werewolf after Grady hears stories about him from his friends Will and Cassie, though his father told him he's harmless. He didn't make a positive impression when he played a prank on the children, laughing and shouting "I'm the werewolf!" while chasing them. After it's revealed that Will was the werewolf and was chased off and killed off by wolf, the swamp hermit found Grady, wounded by an attack by Will and took him back to his house.
In the TV show, the swamp hermit captures Grady in a net, believing him to be the werewolf. He finds out he was wrong when he realized that Grady didn't change under the full moon. Later that night, he finds out who the real werewolf is and tries to capture it in the net again. He shouted at it, "You took my wife and children, everything I ever loved! I swore one day I would take your heart the way you took mine!" But he realized, to his horror that it wasn't the werewolf, it was a deer. Will killed him after he told Grady to run for it.
What happened in the episode was likely non-canon.
The Swamp Hermit has wild grey-white hair that stands up in all directions. He usually wears very ragged and dirty clothing.