Percy Wetmore is one of the death row prison guards in the Stephen King novel The Green Mile. Percy is described as a small (in both body and mind), man, who works on death row for the pleasure of wanting to see prisoners die. The other guards want him reassigned because of that, but his contacts enable him to stay on the Green Mile. Percy is an instigator, stirring up trouble with his violent behavior. Eventually he sabotages an execution, because he wants the condemned prisoner to suffer as he dies. He succeeds in his quest. He is therefore unofficially punished because of it by the other guards, but shows no remorse in the end.
John Coffey turns him into a tool for his purpose of killing William Wharton for his crimes and in order to punish him for his crime. He never recovers from that, which was also his purpose and ends up in an asylum for the rest of his life.