Scarecrow

Character Overview
Dr. Jonathan Crane was a psychiatrist at Arkham Asylum who used his fear toxin to make many criminals insane. This would place them in Arkham Asylum rather than in regular prison.

Batman Begins
Scarecrow partners with Ra's al Ghul in Batman Begins to release the fear toxin all over Gotham. On multiple occasions he tries to get rid of Rachel Dawes, as she is the assistant district attorney and is a risk to the operation.

The Dark Knight Rises
When criminals take over Gotham, Scarecrow serves as the judge, jury, and executioner for all people who are wealthy or in law enforcement who oppose the criminals.